PG - Purge system with oxygen monitoring

Most composite autoclaves utilize nitrogen as the pressurization media.   After a cure cycle, there is a need to purge the nitrogen from the autoclave and bring in fresh breathable air prior to allowing personnel to enter the autoclave.  

In the past many companies have purged this unsafe atmosphere by putting in place a procedure that required the operators to open the door and run the internal autoclave circulation fan for 5-10 minutes prior to entering.  While this method does adequately purge the nitrogen from the autoclave and replace it with breathable air, it is not an automatic function and relies heavily upon the diligence of the operators and supervisors in the production area.

ASC strongly recommends the use of an automated purge system for all walk-in autoclave that utilize nitrogen.  The PG - purge system option includes the following:

• One (1) high-pressure purge blower, rated to delivery breathable air to the autoclave (19.5% oxygen) in under 30 minutes.
• One (1) high-capacity purge air inlet valve.
• One (1) high-capacity nitrogen outlet valve
• One (1) Safety blow-out box
• Air sampling pump and air sampling valve(s) positioned to sample autoclave air.
• Oxygen monitoring instrument
• Door interlock to disable door open operation until 19.5% oxygen is monitored at instrument.

Multi-point sampling

For small and mid-size autoclave, the sampling system utilizes a single connection at the rear of the autoclave, however for longer autoclaves, ASC incorporates multiple sampling valves that will sequence and repeat to insure safe oxygen levels at different points down the length of the autoclave.

Air sampling and monitoring

The integrated oxygen monitoring system automatically samples the autoclave at the end of a cure cycle and confirms safe oxygen levels prior to allowing autoclave door operation. 

The monitoring instrument, manufactured by AMI Devices, has a 10-year sensor and displays the oxygen percentage for the operator to view.  The monitor is also connected to a stack-light which illuminates Red when it is unsafe to enter and Green when the purge cycle has reached a minimum purge time AND the oxygen level has been verified to be at least 19.5%.

In order to provide an even safer system, ASC incorporated a flow monitoring sensor to guarantee that the sample pump is operating properly during the monitoring period.   ASC is the only company to have this feature.

Additionally, the sampling logic is designed to require that the autoclave fan is running during a purge sequence.  If the fan is stopped prematurely, the purge cycle will fail.

Purge completion time

Although there is no specific industry standard, most purge systems are designed to achieve safe breathable air in less than 30 minutes.  If you require a shorter purge sequence, please contact ASC sales engineer to discuss other custom options.  Note that reduction in purge time can cause the price to increase dramatically.

Back-pressure blower safety

Although a purge system is a recommended safety system for the autoclave, an incorrectly designed purge system can cause catastrophic failure and injury if the purge air valve were to open while the autoclave is fully pressurized.    This has happened a few times in the last decade on autoclaves built by some of our competitors, and the result has been a catastrophic failure of the purge blower and explosive shrapnel.  

In order to mitigate the risk of blower back-pressure, ASC’s purge system incorporates a series of a safety features that include a hard-wired pressure interlock for the fresh air valve, a single-acting actuator for the valve, and a proprietary blow-out box which will relieve and vent excess-pressure in the unlikely event that the valve opens.