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Troubleshooting a 6.5 Pressure Hold Pot w/Thompson Valve

There are 3 main culprits (usual suspects) when experiencing difficulties with your pressure hold blast pot.  In this article we cover the solenoid, auto air valve, and Thompson Valve.

The Solenoid


  • The blast nozzle is stuck open
  • No abrasive is released — only air gets to the nozzle

With the above symptoms, the first place you should troubleshoot is the Solenoid. The Solenoid controls both the air and abrasive supply as well the general mechanics of the pot.


  1. First determine if the solenoid is working. When you activate and release the deadman handle you should feel a puff of air coming through the muffler on the back side of the solenoid. This indicates that the valve is opening and closing successfully.
  2. Remove the ‘air out’ line from the solenoid.  This is the line that goes to the Thompson valve. Now, when you activate your deadman handle, air should come back through the return, and activate the valve – but no air will be sent to the Thompson.
    1. If the solenoid is working correctly, air should simply escape through the outlet.  You can move onto investigating the Auto Air Valve (see below).
    2. If air does not escape the solenoid, you should check the deadman handle first. If the deadman is working correctly, there is most likely debris built up inside the solenoid that is preventing its activation.

Solution: If debris is discovered, remove the 4 screws and pull the internals.   Clean and replace the o-rings as required or purchase an Axxiom replacement kit.

The Auto Air Valve

  • Blow-by air out of the nozzle
  • No air at all in the blast stream, only abrasive
  • Hose chugging
  • Nozzle continues to leak blow-by air when disengaged and laying on the ground

If the solenoid works, the next component to troubleshoot is the auto air valve.


  1. Simply turn the choke valve from the ‘on’ position to the ‘off’ position.
    1. If the air stops, we know the problem lies with the auto air valve.
    2. If the air doesn’t stop, you’ll need to check other components of the auto air valve (choke handle, etc) before continuing to the metering valve

Solution: If the auto air valve is the problem it will need to be replaced.  If not replaced, it will eventually fail and compromise productivity.

The Thompson Valve

  • Blast nozzle keeps blasting
  • Chugging abrasive (no air) when deadman is activated
  • After brief delays in blasting, the hose chugs out abrasive when restarting
  • Blow-by air is escaping

If the solenoid and auto air valve are properly working, the next likely culprit is the metering valve.


  1. Fully close the inlet valve to the Thompson valve. This stops the abrasive supply.  If air no longer escapes from the nozzle, the problem lies with the Thompson valve.

Solution: When a Thompson valve overloads your hose with abrasive or doesn’t shut down, it is most likely stuck open.  It will need to be removed, disassembled and inspected.  Possibly replaced.


These suggestions should help you troubleshoot problem in the field and hopefully diagnose the cause of your issues.  Should you need assistance or further clarification, you can always give BlastOne a call and consult with our technical team.

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