autoclave steam by priorclave

Frequently Asked

autoclave frequently asked questions on steam autoclaves answered by priorcalve

Find the Answers to Your Questions

Below you’ll find answers to some of the more common questions asked about Priorclave’s autoclaves grouped by topic. Don’t see an answer to your question? Contact us.

About Us
Our Products
Choosing an Autoclave
New Owners
Customer Service
About Us

Where are the units assembled?

Priorclave manufactures everything at their London facility, and unlike most manufacturers, produce all their own pressure vessels in-house.

What is the overall size of the company worldwide?

Thirty people at the factory, which is a debt-free family-owned small business with approximately $8M in annual revenue.

How long have Priorclave been in business?

30 years

Our Products

Are vertical or horizontal sliding doors available?

When it comes to steam-operated appliances, the fewer the number of moving parts, the better. Our door is a simple, proven hinged design with a thick-gauge silicone gasket. But if your application necessitates a powered or sliding door, we can certainly accommodate you.

What is "Gravity Fill"?

This refers to having an automatic water fill system where the filling tank is set down low so that the controlled water level in the tank matches the desired fill level in the autoclave. We call it “freesteaming.”

The idea is that while the fill valves are open then the water level in the autoclave balances out to fill to the same level as is in the tank.

This was offered and fitted partly due to the misunderstandings to do with water purity as it does not require a conductivity probe to detect the upper filling level. We now fit automatic water fill models with lower and upper level sensing probes.

Is Overheat Protection (Fault Code F003) fitted to my Priorclave?

Overheat Protection (fault code F003) is a standard feature on all Priorclave models: The Tactrol control system monitors the autoclave temperature control probe. If it exceeds 142ºC (roughly 280ºF) then the program is aborted and the F003 overheat error code is displayed.

What is the heat output of each model?

Some facilities may be concerned about the impact their autoclave has on the building HVAC system.  Although the heat output from the autoclave is cyclic and varies throughout the cycle, a good rule of thumb for the thermal load placed on the HVAC by the autoclave is that it will be equal to roughly one third of the total heater power of that model per cycle.  (Engineers at our London factory have compiled this Power Ratings and Heat Dissipation Table. If the autoclave is steam heated from an external supply, you can use the heater power of the corresponding electrically heated model as a basis for estimating the thermal load.)

Models with internal steam generators (although heavily insulated) will give off a little more heat, since the generator runs throughout the cycle and even when the autoclave is not in use. Models with a steam jacket will give off a little less heat, because the jacket is insulated, and if water cooling is used the heat is ideally shunted out the drain.

How much water does each model use?

Although it is impossible to say how much water an autoclave will use without knowing a great deal about your operation, we can offer a rough guideline.  As a rule, benchtop models with condensate bottle exhaust will consume as little as ½ liter per cycle.  Models with drain condenser exhaust cooling will consume 15—25 gallons per cycle.

In the interest of accuracy, we gathered the following data by monitoring water consumption on an autoclave with a fairly popular laboratory configuration (a 150L Priorclave front-loader with a vacuum system and drain condenser) running standard sterilisation cycles:

Autoclave Use: On average for a normal cycle, around 3.3L is lost as vented steam from the autoclave chamber.  This is replenished by the water fill system at the end of the cycle. (The water holds around 12L.)

Vacuum Pump Use: This varies widely by cycle type, but on a cycle with the standard two pre-heating vacuum pulldowns and 12 post-cycle vacuum pulldowns, around 35L of water is used per cycle. If only a pre-heating vacuum is used, then the water consumption drops to around 10L per cycle.

Drain Condenser Use: This also varies by cycle (the condenser is thermostatically operated, and this only runs as needed).  On a cycle with the standard two preheating vacuum pulldowns and 12 post cycle vacuum pulldowns, the drain condenser consumes around 10L per cycle.

Are your pass-through autoclaves air tight?

Our pass-through sterilisers are designed for air-tight fitting through separating walls, allowing for decontamination of material prior to release from the facility. They are also fitted with interlocking doors such that the outer door cannot be opened unless the autoclave has completed a decontamination cycle.

In order to meet effluent retention requirements, our pass-through units can be fitted with an exhaust filtration system that captures all hazardous pathogens: All autoclave exhaust is passed through a 0.05 micron microbiological filter mounted outside the autoclave chamber. Once the door is shut and the cycle is started, unsterilised effluent is returned to the autoclave chamber for sterilising on the next run.

Is the steam generator on board the unit or does it take up a separate footprint?

Going back to our design principle of “elegant simplicity,” we generate steam in the chamber itself. This provides for enhanced steam circulation, excellent water conservation, and reduced service costs by reducing the number of moving parts by a third. The vessel can be drained at the end of each cycle and refilled, or the water can be reused, depending upon your specification.

What is the difference between medical and research-grade autoclaves?

In many areas the autoclave market is dominated by medical-grade sterilizers. These rectangular-chambered units are FDA approved for sterilising high volumes of clean, relatively flat objects on trays (as you might expect in a hospital setting). They are made to run all day, every day. In fact, they don’t like to be turned off or “go cold”—they tend to break down if they are allowed to cool.

Cylindrical-chambered, research-grade autoclaves are intended to remain cold when not in use, and only produce steam on demand. Their cylindrical construction means that they heat and cool quickly—they don’t need much energy or water, and they don’t mind sitting idle for long periods of time. Robust stainless steel chambers, large diameter pipework, and natural steam circulation make it possible to reliably prepare media, process liquids and waste, and sterilise lab equipment. They are also well suited for non-sterilisation applications like quality control and destruction testing.

Priorclave’s research-grade autoclaves feature:

  • Larger diameter pipework and valves
  • In-chamber steam generation
  • Optional pre- and post-vac cycles with actual vacuum pumps—no “Venturi ejectors” or other resource-intensive components
  • Single wall chamber construction—no steam jacket necessary
  • Maintenance relative to usage—no service contract required
  • 3-year limited parts and labor warranty and free lifetime tech support
  • 20-year pressure vessel warranty
Choosing an Autoclave

Do I need a “gravity” or a “pre-vac” autoclave?

In order to achieve proper sterilisation, air has to be removed from the chamber.  Gravity autoclaves allow the steam to displace the air through a port in the chamber. We refer to this process as “Freesteaming.” “Pre-vac” autoclaves use a vacuum pump to actively remove the air from the chamber. Research-grade autoclaves can be configured for either. Gravity/Freesteam and Vacuum stages are not used together.

So long as you purchase the vacuum options, the autoclave is capable of both pre-vac and freesteaming/gravity cycles. You can adjust how you want cycles to run—simply turn off the vacuum pump option to run a freesteaming/gravity cycle.

Can you connect the autoclave to a sink drain?

We can connect to a sink drain so long as it is vented properly (in accordance with plumbing codes) and not too high above the finished floor (relative to the autoclave chamber drain).

Do I need a canopy or extractor hood for my autoclave?

An extractor hood will help reduce steam and heat build-up in the room, and help to reduce odors—particularly if the unit is placed in a small room, or run on a regular basis. If disposable plasticware is being processed, then an extractor hood should be considered, especially if there is a risk of potentially harmful fumes.

That said, please bear in mind that the air handling systems of modern laboratories are quite sophisticated. We recommend consulting with a qualified engineer before making any decisions that may affect building HVAC systems. If necessary, research-grade autoclaves can interface to building systems to provide proper on-demand ventilation.

What is the standard cycle length?

You’d think that we could furnish a chart of typical cycle times based on load type, right? But autoclave companies cannot recommend generic cycle lengths or temperatures, even if we know the density and composition of the load. Not only do many parameters differ by application, but regulations can also play a role in what constitutes an appropriate processing time. Likewise, many universities create guidelines for their own labs.

We can tell you that we see many labs running cycles between 15 minutes and 90 minutes. We also see liquid loads that can take several hours to complete (with natural cooling). Our control system can be set to run cycles of any duration, from 1 minute to 999 hours. Cool-down times are directly related to the mass and density of the load. There are a number of options we can build into the unit to accelerate or control the rate of cooling, as necessary.

Does the unit have preset programs, or can we create custom programs?

As a research-grade product, there are no standard programs. Custom programs can be set—and changed—at any time. Our technical support staff is happy to guide you through the process, if needed.

Can your autoclaves be used for food and beverage products or retort processing?

Any of our autoclaves can be equipped with an air ballast to permit autoclaving of sealed cans or pouches. Many of our food and beverage customers use our autoclaves in this way, but some choose a retort machine (which we do not manufacture) depending on their throughput.

Can a single steriliser be used for multiple load types?

Yes—we can configure preset selectable programs for each of your load types.

Why would we need vacuum functions?

Vacuum functions provide 3 features:

  1. Removes air more effectively from difficult loads (evacuates the chamber during pre-cycle stages)
  2. Accelerates post-cycle stages (pulling the steam out of the chamber to accelerate cooling)
  3. Dries loads (multiple pulses applied in succession can dry glassware, tips, instruments, etc.)

Vacuum functions are not suitable, or necessary, for all types of loads. There is no reason to pay for them if you don’t need them. In fact, if your autoclave is equipped with a vacuum and it goes unused, it could present maintenance issues.

Research-grade autoclaves can create a natural vacuum as they drain–without the use of a vacuum pump–effective for many applications. For example, glassware comes out mostly dry, although a box of tips would require additional drying, which can be provided by a drying oven.

You might consider vacuum options if you run more than five cycles per day on a regular basis, or if you run porous loads (textiles and wrapped instruments) that must come out fully dry.

What is "Automatic Timed Freesteaming"?

Automatic timed freesteaming is a form of gravity displacement.  Initiating at a preset temperature and continuing for a predetermined period, freesteaming allows sterile steam to push the air out of the chamber. This results in more reliable sterilisation of a wider range of loads.

Do pass-through autoclaves have to be certified? If so, to what standard?

Since our pass-through autoclave customers work in a variety of fields—ranging from agricultural research to product development and pathogen containment—it would be difficult to identify a single standard to focus on. What is most important is that an appropriate certification is established, validated, and adhered to.

We encourage the certification of all pass-through autoclaves “as-installed.” Every discipline of science has their own standard (helium, halogen, smoke, etc.). Depending upon the application and environment, we also encourage re-certification on an annual (or more frequent) basis.

Are vertical or horizontal sliding doors available?

Our door is a simple, proven hinged design with a thick-gauge silicone gasket. When it comes to steam-operated appliances, the fewer the number of moving parts, the better!

What is the difference between electrically and steam-heated autoclaves?

Electrically heated (EH) and steam heated (SH) autoclaves both use steam and pressure to sterilise loads. The difference is that EH models generate their own steam within the chamber, whereas SH models can be connected to a “house” or other external steam source.

We typically recommend EH over SH models. Not only are they more reliable and cost effective for research applications, they’re also easier to install and maintain.

I think I see in the literature you have cycles for media vs. cycles for dry materials, is that correct?

Our research-grade products are capable of running all the same cycles as the more complicated medical-grade units.  Since each steriliser shipped is built to order, we omit options you do not require. This increases the reliability of the unit while reducing both the initial purchase price and the total lifetime cost of maintenance and operation.

Should I buy a top or front loading autoclave?

A Top Loader has a smaller footprint and accommodates taller items, but loading/unloading can be more difficult. A Front Loader is easier to load, has better steam circulation, and is more difficult to overfill, but has less usable space for a given volume.

New Owners

How do I open the door?

This is our most frequently asked question—especially from new Priorclave owners. Do not worry! The door can be tricky at first, but the design allows for very safe single-handed operation.

Press the “Door” button on the control panel. There will be a beep and the message “Hold” will be displayed on the digital temperature display. Wait for a short time until the temperature display returns to normal. There will be another beep and the door indicator will light up. Press the Door button once more to release the lock.

Open the door as described below:

  1. Lift the locking handle up.
  2. The handle should spring out into its unlocking position.
  3. Lift the handle fully upwards to unlock the door. The handle is now in its safety lock position, allowing any residual pressure inside the autoclave to escape harmlessly.
  4. Nudge the handle down to release it from the safety position.
  5. Push the handle in as far as it will go.
  6. Move the handle fully upwards to its parked position.
  7. With the door unlocked, carefully pull the door open.

For illustrations on how to open the door, please refer to the Operation Manual that you received with your autoclave.

Where can I find my Pressure Vessel Certification?

A copy of the manual was sent to you along with your autoclave. The Pressure Vessel Certification can be found at the back of the manual for the autoclave. If it is not located there, please contact us and we will be able to send you a digital copy.

Where is the Operation Manual?

All Priorclave sterilisers arrive with their Initial Opening Instructions and Installation Manual attached to the outside of the unit. The model-specific Operation Manual is in the chamber of your Priorclave. If you have lost any of these, you can find PDF versions in the Downloads section of our website. Replacement manuals can also be ordered by contacting us directly.


How much space around the autoclave is required to service it?

Because of their efficient design and construction, our wheel-mounted units are significantly easier to maneuver than traditional medical-grade sterilisers. We recommend making all service connections with flexible braided stainless-steel hoses. This allows the unit to be rolled out for service (just like a refrigerator or other appliance) then tucked away when the work is done.

For room planning purposes: How much steam and heat will the unit give off during a typical run?

For best results (and the most pleasant work environment), install your autoclave in an air-conditioned, well-ventilated space.  All autoclaves release steam and heat during their process cycle, and this should be taken into consideration when choosing a site in your laboratory in which to install your autoclave. Regardless of insulation arrangements employed to reduce the temperature of the autoclave, the outer casing of all autoclaves will emit heat into the work area. For the comfort of staff, it is recommended that autoclaves are installed in air conditioned areas. Heat output from the autoclave will vary at different stages of the cycle.

For the purpose of calculating the load placed on the air conditioning system by the autoclave it should be adequate to allow for a figure of one third of the total heater power of the autoclave per cycle, although the actual output will vary according to the autoclave settings used. Heater power refers to the power of the heaters in kW. On 230V the heater power will be 3kW, on the compacts and on the 100, 150 and 200L models (top and front loading) the heater power is between 7kw or 10.5kW, and heater power is 18kW on the Q63 models. (This information can also be found on the specifications page of all manuals. Although the heater power will be lower at lower voltages, if in doubt, use the higher value for calculations.)

Air-cooled autoclaves cool more quickly in a cool room, and therefore high room temperatures will increase autoclave cycle times. This can become particularly problematic if the ambient temperature exceeds 95ºF (35ºC).

If correctly installed as described in the installation manual, there should be no steam emitted to the work area during operation. There may, however, be some steam emitted when the autoclave door is opened. Under normal circumstances, the thermal cooling lock will prevent the door from being opened until most of the steam in the chamber has condensed; however, under certain circumstances, such as when the thermal cooling lock override is used, significant amounts of steam can be released. Consideration should be given to how this steam may affect your facility’s smoke and heat detectors, other equipment, etc.

What is the temperature of the discharge steam/water?

There are many factors that affect the temperature of the discharge steam/water. With no drain condenser fitted, the autoclave will be purging steam up to 121°C. All discharge will be through the vent outlet pipework. The autoclave can drain its water if drying options are fitted—this will drain the chamber after process countdown, with temperatures as high as 136°C.

With a drain condenser fitted, the water temperature will be approximately between 40°C and 60°C. Please note that water can be drained through the manual drain at any temperature.

Can one water softener be used for two autoclaves?

Depending on the output of the water softener used and the size of the autoclaves, the answer is yes. The water softener sold through Priorclave is a mid-range unit specified to be suitable for the smaller home with one bathroom and a standard “combi boiler” or gravity-fed hot water system. These softeners are also quite useful as they require no electrical installation as the recharging cycle is controlled by a water pressure powered clock mechanism.

The water output capability of our softener is specified as 20L per minute with a minimum of 0.6L per minute and a maximum of 31L per minute. This is more than enough to run an electrically heated autoclave, because we are only looking to replace between 0.25 and 40L (depending on the model and the type of cycle being run) within 10 minutes every few hours or so, and with the head start of a header tank on the back pre-filled with softened water.

If you choose to buy your water softener from a third party, we normally recommend the GE GXSH40V, which can be found at home improvement stores. It is capable of 35L per minute and is more than sufficient.

What is the maximum and minimum allowable pressure at the water input of the autoclave?

We specify a minimum pressure of 3 bar and do not recommend going above 6 bar.

The water pressure in our test bay is barely above 1 bar and generally the autoclaves will run on this for testing purposes (we are not worrying about the output temperature of the autoclave exhaust). We will sometimes notice the low water pressure if there is a high demand (usually vacuum pump, steam generator filling pump and condenser running at once) and this shows up with the vacuum pump cutting out intermittently when the feed tank can’t be filled quickly enough and the tank water level drops to below the level of the level switch in the tank.

Is it possible to run the unit without being plumbed in?

Yes, all of our non-vacuum models can be configured to be “plug-n-play,” with only an electric cord connection. Benchtop models can also be placed on mobile carts, to be rolled from one area of the lab to the other.

Should we have our water quality tested?

When in doubt, it’s always best to have water tested. This can save you thousands of dollars in service costs, and greatly extend the life of your autoclave. Using a hard water supply will lead to a build-up of scale that will damage the heaters and other parts of the system, and could invalidate the warranty.

If in the first six months of operation you observe hard-water scale or other water-quality related issues, refer back to the Installation Manual and have your water quality tested. You can always contact us for advice on how to proceed.

Even “soft” water supplies contain trace minerals. These will slowly accumulate in autoclave chambers and plumbing, and on heating elements. Scale build-up will significantly impact autoclave performance and decrease operational lifetime. Distilled white vinegar (available at any grocery store) can be used to effectively address scale accumulation. See your Operation Manual for details.

Should I connect my autoclave to soft water or purified water supply?

Soft water is the most reliable, and least expensive, source for sterilisation. Purified water is best suited for specialty applications like medical device or GMP production. Because it is highly corrosive, purified water requires stainless steel pipework, which is quite costly, and even then presents additional challenges for proper maintenance. Research-grade autoclaves can be configured to use either common soft water, or purified water.

Because Priorclave autoclaves use water conductivity to detect the water level in the chamber and protect the heaters the use of deionised (DI), pure, or distilled water is NOT advised. Additionally ultra-pure water has a corrosive effect on the copper pipework and brass fittings used in the autoclave. We recommend the use of a softened water supply to protect the autoclave heaters from the effects of lime scale.

For more information about water quality, check out our paper Priorclave Water Quality Requirements.pdf.

Can we connect our water softener to the autoclave’s drain condenser system as well as the water-fill tank?

Yes, you can do so if you choose—but please read the previous question and answer in order to be sure you want to do this.

Why are there two water connection points on my autoclave?

Many areas have hard water (which we discuss at length over the next few questions; scroll down to learn more!) In order to protect the autoclave’s in-chamber heaters from limescale, we recommend you use a water softener. But your autoclave may have ancillary equipment (such as drain condensers and vacuum pumps) that consume water, but do not need a softened water supply. In fact, they may function better when directly connected to the municipal water supply. As a result, in some cases, we build units with two water inlets: One for the water softener connection to the steam-generation system, the other for the ancillary equipment to connect directly to the municipal water supply.

In general there is no harm in using a softened water supply for ancillary equipment, if you keep the following factors in mind:

  1. The volume of water used by a vacuum pump or drain condenser is fairly high. You’ll need to account for this high demand and choose a larger water softener to accommodate it.
  2. Vacuum pumps need decent water pressure to run efficiently.  A direct connection to the municipal water supply will tend to have higher pressure than a connection plumbed through a water softener.

Water pressure is not critical for the water filling system used by the autoclave for sterilisation, which is why it can be reliably supplied by a residential water softener.

Should I connect the safety valve outlet to a drain?

Unlike some other steam heated systems the safety valve does not operate during normal running. It should actually never open at all except during routine annual testing.

We strongly recommend that the safety valve outlet of the autoclave is left OPEN so that, in the event of a malfunction, the excess pressure is expelled without hindrance and the main pressure vessel is safe and avoids potential catastrophic failure.

This arrangement also gives an audible and visual indication to operators that there is an issue with the autoclave.

We suggest that if any pipework is fitted to the valve outlet that this is only to direct the output of the valve to the floor with the minimum number of turns possible so as to ensure free flow.

Do I need a drain to connect my autoclave to?

Yes, if used for processing contaminated materials or if the autoclave has any form of active air removal system. Exceptions are rare. Please refer to our Guide to Autoclave Installation for more details.


Our facility will not be using the autoclave for a few months. What do we need to do to prepare the autoclave to sit for an extended period of time?

Our factory recommends draining and cleaning out the chamber to prevent mold growth. You can also turn off the power on the autoclave at the isolator (the big red switch on the back). The main processor board has a built in battery (like the motherboard in a computer), so your settings will be saved.

A few notes:

  • If you do leave your autoclave without power for a few months, the controls may be sluggish when it is first started up again. It should go back to normal after a couple of cycles.
  • If your autoclave has autofill, it automatically tries to refill itself every time the door is opened. The easiest way to drain the chamber is to turn off the power at the isolator switch while the door is opened, then use the manual drain at the back to empty the chamber.
  • It may be a good idea to perform maintenance when you are ready to start using your autoclave again to ensure that all valves and components are functioning properly.
    You may also need to take care of your water softener if you have one. What you need to do can vary depending on the type of softener you have, so it will be best to follow the manufacturer’s instructions.

What chemicals, agents, and materials should not be autoclaved?

Although this is not an exhaustive list, the following things need to be considered when deciding if items can be autoclaved:

  • Is this intended to be a re-usable item? If so, then you must consider the material that the item is made from. Any material that will not withstand the set sterilising temperature (usually between 121º and 134º) should not be autoclaved.
  • Volatile flammable items should not be autoclaved in a standard laboratory autoclave—especially those with heaters within the autoclave chamber (as is the case with most Priorclave units shipped). 
  • Even with non-flammable chemicals, you should note whether the chemical is likely to degrade silicone, Viton, or other high-temperature rubbers. Your Priorclave’s seals and gaskets are made of these materials, and may be damaged if you process such chemicals.
  • Regarding corrosive chemicals: the chambers of all Priorclaves are made of corrosion-resistant grades of stainless steel—nonetheless, we still recommend avoiding routine exposure to corrosive chemicals like hydroxides and chlorine.
  • Think twice before autoclaving radioactive materials. These can accumulate in the valves and pipework, creating hazards when servicing the autoclave at a later date or when disposing of valves and pumps that may need replacement during the life of the autoclave. In addition to this, radioactive material may be carried out in the autoclave exhaust and drain into the drainage system. Despite what you have learned from the Spiderman and Incredible Hulk franchises, the slapdash dissemination of radioactive material generally has wholly negative outcomes for all involved.

What is the operating range for Priorclave autoclaves?

The pressure vessel is rated up to 138°C, but the safety valve is set for 136°C (per ASME).

How does the Manual Drain Work?

The manual drain can be used to remove the standing water from the vessel during the course of weekly or monthly maintenance. The procedure is as follows:

  1. Unlock and open the manual drain with the key provided.
  2. Drain the standing water into a floor sink or other receptacle.
  3. With the vessel empty, clean the heating elements with a damp cloth to remove any build-up or lime-scale and prevent the accumulation of spilled media or potentially corrosive chemicals.
  4. Close and lock the manual drain.

Alternately, a wet/dry-type vacuum cleaner (i.e., any of the many “shop vacs” sold at home improvement stores) or a siphon pump can be used to remove the standing water.

We have Bowie-Dick Test Packs that we are required to use to test for complete air removal. What are the best settings for this?

There are several schools of thought on the Bowie-Dick test cycle in the United States. It was very common to run it at 134—135°C for 3 to 4 minutes. The test was widely used in the healthcare industry for years. When it became a desired test for the life science industry there were several test packs developed for a lower temp and longer time, due to the fact most pharma units run typically at 121.1°C.

The test parameters should be set to whatever the pack manufacturer states. If the pack isn’t validated by the manufacturer to run at 122°C, then it should be run at the higher temp and shorter time. Usually any pack designed for 122°C requires that it be run for 8 minutes, give or take a few seconds. If all of your products run at 122°C, the lower temp on the test pack makes sense. The bottom line is that the 122°C for 8 minutes is probably appropriate for your test pack. It may not pass at 4 minutes of exposure.

The Drain Condenser System occasionally makes banging noises, usually during the cooling stage. Should I be worried?

There is no need to be too alarmed by these types of noises. Within the condenser and pipework there will be a constantly changing mix of hot steam and cool or cold water, and the mix will create differing gaseous pockets at different stages within the pipework. It may not be consistent between different autoclaves as it very much depends on a host of variables such as pipework length, route, size, temperature of water and steam, and even minor manufacturing differences.

There are no moving parts or excessive pressure within the system, so it is perfectly safe.

Can I use DI or distilled water with my autoclave?

Priorclaves can be specified to use any type of water source, but most are built to operate most effectively with standard softened water. A unit specified for standard water may not function efficiently—and can even be damaged—by demineralized, deionised (DI), distilled, reverse osmosis (RO), “high-purity”, or ultrapure water (UPW) supplies.

I’m using Media Warming on my autoclave, but the media is not fully liquid when I open the autoclave. Can I adjust the set temperature for this function?

Yes. Although this is a simple operation (only requiring a few minutes), changing this Tactrol parameter requires some guidance. Please contact support, and we’ll walk you through making this adjustment. Such assistance is covered by your autoclave’s free lifetime technical support.

I want to start my autoclave cycle before I arrive in the morning, is that possible?

Yes! Delayed Start is standard on all Priorclave models, and can be set from the Tactrol control panel. Please refer to your Operation Manual for a full list of functions and settings. You can also find the Priorclave Customer Setting Instructions sheet in the Downloads section of the Priorclave website.

What impact does our autoclave have on our facility’s heating and cooling system?

Because it harnesses high temperatures for long periods of time, any autoclave can have a major impact on your building HVAC system. Some aspects of Priorclave’s design (such as cold idling) mitigate this impact. Our team works hard to guide every autoclave buyer to a properly specified and installed unit. This minimises the impact on HVAC operation.

In general, the thermal load placed on your air conditioning and ventilation systems by your autoclave is approximately one third of the total heater power for the unit’s first hour of operation. The output from the autoclave is cyclic and varies throughout the cycle, but this figure is a good guide for a thermal load calculation. If you’re using a direct steam heated unit, look up the wattage of the corresponding electrically heated unit.


My printer is using a lot of paper. Can it be set to print out less often?

Yes, you can change the print interval. By default it is set to print relevant data every three minutes during the cycle dwell period. The print interval is one of the many functions that can be changed from the front control panel. Please refer to your Operation Manual for a full list of functions and settings. As a quick reference, you can find the Priorclave Customer Setting Instructions sheet in the Downloads section of the Priorclave website.

My printouts are showing the wrong time. Can the time be adjusted?

Certainly! The time and date settings (along with other common functions) can be adjusted directly from the Tactrol control panel. Please refer to your Operation Manual for full instructions. As a quick reference, you can find the Priorclave Customer Setting Instructions sheet in the Downloads section of the Priorclave website.

When I press START the autoclave beeps and fault sign lights up. No codes are displayed. I’ve checked all the obvious things but please could you advise?

This scenario sounds like one of the START criteria has not been met. (The Autoclave control system requires a number of parameters to be met before it is considered safe for the Autoclave to start a process cycle.) Please check the following:

  1. Is the door correctly and fully closed?  There are several micro-switches that monitor the door position. Opening and then firmly closing and sealing the door should remedy this.
  2. Does the pressure gauge read zero?  Open and then reseal the door.  The gauge should now read zero. If this gauge reads anything other than zero on an idle autoclave that has just been closed, it implies that there is a fault with the pressure switch or the pipe-work between the switch and the vessel.
  3. If you have in-chamber heating, are the Low Water Probes clean and is the water level touching the highest probe?  If the probes are dirty or the water level is too low, the autoclave will not start.

If these steps fail to remedy your problem, please contact support for further assistance.

When I press START nothing happens and no LEDs on the “half-moon” cycle progress display light.

This is because the Tactrol Control System is waiting for a response from the printer before starting the heater. Either the printer is not installed correctly, or the connection to the printer has been lost. Please follow this procedure:


  1. Simultaneously press the up/down buttons directly below the green dwell time display. The autoclave should beep. The temperature display will change to “0” and the dwell time display to “000”.
  2. Press the up button below the dwell time display until it reads “011.”
  3. If the temperature display is showing anything other than “0” adjust it down to “0” using the up/down buttons below the temperature display.
  4. Now reset the controller. If your autoclave includes a Multi-Program Memory unit, turn the Setting Lock key from position 1 to position 3 and back again. If you do not have a Setting Lock key switch, then reset the controller by pressing the small black reset button labeled “Tactrol Reset” located at rear of control panel.

The autoclave should now function correctly. If not, please contact support.

The thermal lock is set to 80°C but the autoclave will not open until the temperature is 50°C. How can I reset this to 80°C?

This is the intended behavior of your autoclave, and is for your safety. The thermal lock is fitted as a safety measure and has become standard for all laboratory autoclaves after a number of accidents where glass bottles containing liquids or growth media exploded on exposure to cold air when the autoclave door was opened. The standard requires that the door cannot be opened when the temperature of the load inside the autoclave is above 80°C.

Liquid loads, as a rule (thermodynamically speaking), cool much more slowly than the autoclave chamber. Based on our experience and measurement of a variety of different loads, we’ve found that the control probe needs to be approximately 30 degrees below the desired 80°C safety threshold in to be sure that the load itself is at or below 80°C. This is why thermal lock releases when the temperature of the interior of the autoclave reaches 50°C.

The thermal lock is a safety guard that we have set to this temperature to ensure that all load types and conditions complete the sterilisation cycle safely, from the time the door closes to the time it opens. It is possible to override this safety feature. Contact us for a waiver and further details.

The temperature display is showing “F00” and a number, and “FAULT” is lit on the panel (there may be other messages lit as well). What does this all mean?

Something is wrong. A complete list of error codes is included in your Operation Manual. If your autoclave includes a printer, the code and a short explanation will be printed out. Alternatively, you can find a list of error codes in the Downloads section of the Priorclave website.

The Service Fault Light has just come on. What does this mean?

The Service Fault Light comes on every 6 months or once 500 cycles have been completed. This means that it is time for Preventative Maintenance to ensure the continuous operation of your autoclave. Please contact us for support and we will send a trained technician to work on your autoclave!

Customer Service

We have an autoclave that hasn’t been used for some time and would like to have it up and running again. Have you any advice on the appropriate site to install it and some of the health and safety considerations that need to be taken into account?

First, take a look at our Guide to Autoclave Installation.  This document offers a solid foundation in autoclave installation.  Depending on your circumstances, what is being autoclaved, how often, and other factors, you may determine you need some guidance in finding the right solution for you. For more detailed assistance, please contact us directly.

For new installations in the UK we can often arrange for one of our Service Technicians to come and look at your proposed installation site and give practical advice. For installations outside the UK, we can often arrange for a similar consultation with your local authorized distributor or one of our factory-certified authorized service agents (ASAs).

In terms of health and safety, if you are unfamiliar with running autoclaves, please refer to the Health and Safety Executive’s Guidance Note PM73, which covers all aspects of laboratory autoclave safety.

Is on-site training available for your autoclaves?

We offer training on the use of Priorclave autoclaves and on autoclaving principles. Please contact us for a quote.

What is the availability of spare parts?

Many parts (seals, solenoids, valves, etc.) are standard and can be purchased from many different suppliers. Priorclave also furnish replacement parts, and maintain a “fair price” policy on all components (including our Tactrol Control System), offering these at competitive prices.

Are the parts non-proprietary and available from common sources if we have problems?

We make every effort to use only non-proprietary components available from common sources. The only exceptions to this are our Tactrol Control System and the pressure chamber itself (which is hand built under an ISO 9001:2008 quality management system, ASME-stamped, and tested to 1.5 times the maximum working pressure).

The current Tactrol Control System is the culmination of nearly three decades of development and refinement. It offers unparalleled safety, reliability, and flexibility (with dozens of individually controllable parameters per program, including Cycle Repeat with up to 999 iterations and optional custom Remote Cycle Monitoring).

Am I legally obligated to have my autoclave examined regularly? How often? Can Priorclave carry out such an examination?

In the United Kingdom, yes, you are. It is a requirement of the UK Pressure Systems Safety Regulations that all pressure equipment is regularly examined by a surveyor working for a competent body (usually arranged by your building insurer). This inspection should take place at a maximum of 13 month intervals (i.e., annually).

Although as the manufacturer of the equipment Priorclave are not permitted to carry out these inspections, for customers with a maintenance contract one of the routine visits can be organised to coincide with the surveyor’s visit so that the autoclave has been serviced in preparation for the inspection and our technician is available to assist during the inspection.

This can also be arranged as a one-off service visit, if required. Please contact Priorclave Service for details and a quotation.

For autoclaves installed outside of the UK regulations vary from one country to another, but usually require some form of routine inspection. Check with your insurer to find out what is required in your jurisdiction. Your local Priorclave distributor may also be able to assist you with this.

If I need service, do you have reps in my area?

Priorclave support a global network of exclusive distributors, with sales and service offices throughout world.  These organisations are fully trained by Priorclave to handle every aspect of autoclave specification, installation, and maintenance, and are also intimately familiar with concerns unique to your region.

In addition to your local exclusive distributor, many regions are part of our global network of factory-certified authorised service agents (ASAs).  Even if your Priorclave exclusive distributor isn’t nearby, a Priorclave ASA may be much closer than you think. If your locale lacks an exclusive distributor or local ASA, don’t hesitate to contact us directly:  Our name is on the front of the autoclave, and we stand by that name, supporting every single Priorclave lab autoclave worldwide.

Priorclave can offer 24-hour response, on-site technicians, training for your in-house or preferred third party provider, or remote diagnostic support, all backed by our unlimited lifetime transferable telephone technical support guarantee.

How often should my autoclave be serviced?

The routine operator maintenance includes daily, weekly, monthly, and biannual tasks (these tasks are mostly just keeping the unit clean and occasionally greasing the door gasket). For most applications and facilities, this is sufficient to keep your Priorclave running in good order. For peace of mind, many Priorclave users choose to have an autoclave check-up every six months (a service included with our standard Preventative Maintenance Autoclave Service Plans).

What is the warranty associated with this unit?

All Priorclave autoclaves come with a 12-month limited parts-and-labor warranty, a 10-year pressure vessel warranty, and unlimited lifetime technical support. A variety of Extended Warranties and Preventative Maintenance Contracts are available.


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