Frequently Asked Questions


We have compiled a list of the questions that are frequently asked, in the hope that it might be helpful to our customers. But don’t hesitate to contact us with any questions, comments or concerns — by email at, or by phone at 1-800-444-4351.

  1. Section

    Q: How do I find my serial number?

    Every Herkules Paint Gun Washer has a unique serial number for the unit, along with a serial number for each pump.

    When contacting Herkules for assistance, having these numbers ready is important. The paint gun washer serial number is on a plate or sticker, usually affixed to the unit’s leg.

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    Q: Why won’t my Paint Gun Washer start?

    There are several reasons why your washer might not start; we suggest you:

    1. Check that the air-line is properly connected with 90-120 psi.
    2. Check the lid, and ensure that it is fully closed.
    3. Make sure the limit valve (also known as the MC switch) on the valve bracket is closed in the downward position.
    4. Check all air connections to ensure that there are no leaks.
    5. Make sure the timer cam is engaging the limit valve on the pump housing assembly.
    6. Make sure the timer is on and functioning properly.
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    Q: Why won’t my Paint Gun Washer shut off?

    There are several reasons why the washer won’t shut off:

    1. The timer cam (#M230-001A) may be jammed. If it is not is moving, slightly loosen the nuts holding the limit valve (#M1C) on the top panel of the pump housing assembly. Reposition valve and tighten nuts.
    2. The limit valve (also known as the MC switch) may be stuck in the open position. Please make sure it is closed.
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    Q: My Paint Gun Washer starts, but pumps slowly, or not at all.

    We suggest that you:

    1. Check the Intake Filter (#12491) to make sure it is not clogged. If it is, clean or replace.
    2. Check that the air-line is properly connected with 90-120 psi.
    3. Check all air connections to ensure that there are no leaks.
    4. Drain filter-regulator of water; see Preventative Maintenance in your manual for instructions.
    5. Check the solvent, there should be 5 gallons of clean solvent in the gun washer, with the solvent filled to an inch above the intake filter(#12491)
    6. Check that that lid is closing completely.
    7. Check the limit valve (MC switch) on the valve bracket (M1SA) to make sure it is closed in the downward position.
    8. Check the manifold nozzles and stem supports and make sure they are not clogged.
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    Q: Why does the pump still operate after the timer has shut off?

    The blue and black air lines going to the M1C switch might be reversed (on backwards). Switch the lines, and see if this solves the problem.

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    Q: Why is my 338 Pump not working correctly?

    If the 338 Pump is not functioning correctly, there are three quick checks that can either resolve the issue or help determine if the pump needs to be replaced.

    1. Check the Pump√ The pump can be checked with a brief test, without detaching the pump from the paint gun washer. Attach an air line to the inlet on the side of the pump (see picture). Run the air; if the pump runs normally, then the pump is operational. If the pump is running slow, make sure that the air line hoses are not twisted, kinked or bent.

    2. Check the Regulator√ Unscrew the bowl on the bottom and make sure the bowl is clean. Then make sure that the regulator is set to 75 psi; if lower than that setting, there will not be enough power to operate the pump.

    3. Check the Switches√ Herkules gun washers have two MC switches, which are slightly taller than a paper clip. (The first M1C switch activates when the lid is closed; the second M1C switch is activated by the timer knob.) When the top of the switch is depressed, air flows through the switch, which activates the pump. Make sure the switch can open, and is not obstructed in anyway.  Each switch has two ports (on the bottom) where air lines are attached. If the air lines are in the wrong port, the pump might run when the lid is open. To change the lines; simply push down on the black ring around the port to release the line, then switch and re-connect.

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    Q: My washer unit is great, but the pump is old; should I purchase a new unit, or can I upgrade the pump?

    Most new Herkules Paint Gun Washers use our powerful 338 Pump; this reliable unit can be retro fitted to most washers. In some instances, we provide kits that enable shops to repair their current pump, or convert it to the 338. Current and retired pumps are pictured, along with the kits available for each. To order a new pump, pump kit, or replacement manifold, visit

    Pump Convert/Rebuild/Replace Kit # needed
    338 Rebuild 338-KIT-01
    338 Replace 338
    318 Convert 12164
    318 Replace 318
    314 Convert 11972
    10686 Convert 11972
    10686 Rebuild 10792
    Piston Convert 11981



    338 Pump



    318 Pump



    314 Pump



    10686 Pump



    Piston Pump

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    Q: Why is the pump leaking from its top bar?

    The manifold is probably cracked, but can be quickly replaced. Contact Herkules Customer Service for the replacement part (#1003560), or order online here.

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    Q: Can I clean solvent paint guns with my Herkules waterborne gun washer?

    Only if you don’t want to use it again; Herkules waterborne gun washers are designed to handle the consistency of those paints, and solvent paints will clog and damage the waterborne lines. The G375 and G520 can accommodate both types of paints, because each paint type has a dedicated tank and line. While most Herkules washers can handle both waterborne and solvent, each washer must be dedicated to one paint type or the other.