Several times each year PRIMUS receives calls from the field requesting assistance on how to resolve a “Stuck in Slow Exhaust” problem.

A typical background situation for these calls is that the end user wanted to create a liquids cycle. He/She changed the name to “Liquids”, but did not change all the required setpoints.


When establishing a liquids cycle, two very important setpoints are the “Slow Exhaust Ramp” and “Slow Exhaust Endpoint.”

The “Slow Exhaust Ramp” should be set to between 0.7 and 2.0 psi/min.

Most end users set the “Slow Exhaust Ramp” to around 1.0 psi/min.

PRIMUS recommends a “Slow Exhaust Endpoint” of -0.1 psi or 0.1 psi. Avoid setting it at 0 as this can sometimes cause control issues.

Root Causes and Corrections

Below is a guide on potential root causes of this infrequent, but potentially troublesome problem.

Slow Exhaust Ramp Set Too High

If the new field set ramp rate is set too high, boilover could occur and should be avoided.

Slow Exhaust Ramp Set Too Low

If the new field-set ramp rate is set too low, the sterilizer could get “stuck”. This can happen because opening the drain causes a comparatively rapid reduction in chamber pressure. The sterilizer will then attempt to compensate by opening the steam-to-chamber valve to restore pressure to meet the ramp rate.

If the ramp rate is set too low, the shot of steam will have a tendency to raise the pressure and the ramp will be started again, but at that higher pressure. The process described above will likely repeat itself. The end result will be an increasing pressure in the chamber and the inability to complete the liquids cycle.

If this does occur, the resolution is to stop the steam-to-chamber valve from opening by disconnecting the electrical connector from the valve (do not shut off all steam to the sterilizer as the steam may be needed to maintain the door seal). The pressure will then drop slowly to the “Exhaust Endpoint” and the cycle will be able to proceed to its completion. Once the cycle is completed, the “Slow Exhaust Ramp” needs to be properly adjusted before the next load is run.

Leaking Door Gasket

If the amount of steam entering the chamber is greater than the exhaust rate, the sterilizer can become “Stuck in Slow Exhaust.” The fix is to replace the gasket.

Have a question or having difficulties? Talk to Dave Schall, our PRIMUS sterilizer expert who is here to assist you anytime at 877.679.7800 extension 1212 or email at

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