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Causes of Trouble with and Countermeasures for Spray Guns

Presented here are countermeasures to apply when spray guns are not functioning well.

Possible Trouble

Spray gun does not emit liquid
Liquid leaks from spray gun
User suffers intermittent spraying
Mist drifts upward
While the countermeasures described here apply to nearly all spray guns, there might be some models to which they do not. For details, please refer to the instruction manuals provided for each model. (These manuals are uploaded in PDF format on the page on which spray guns are featured.)
Spray gun does not emit liquid
If air pressure is low, the necessary pressure for piston operation might not be reached.
  Please raise air pressure to the prescribed level (0.2MPa ~ 0.3MPa, depending on the model).
If the piping is narrow and substantially extended, pressure loss will occur. Thus, even if the intention is to provide 0.3MPa, actual pressure could fall to under 0.2MPa by the time it reaches the gun. Even if the solenoid valve's orifice is small, similar pressure loss will occur. If several spray guns are being used and only some of them will not emit liquid, the narrowness of the original piping is often the cause.
If liquid is emitted at first but then fails to be emitted after a while, it is conceivable that compressor horsepower is too low.
Incorrect piping connection
  Have the connections for liquid and for air been reversed? The inlet for liquid is marked “LIQUID.” (The inlet for air is marked “AIR” or “CYL,” which is the symbol for cylinder air for piston operation.) Confirm that this is the case and correct the connections in kind.
O-ring (Y-ring) damage
  If needle O-rings or piston O-rings are damaged, their greased parts broken off, and the needle will not move, please make the appropriate replacements following the procedure specified in the Instruction Manual.
A spray gun with specifications for pressure feeding is being used without fluid pressure applied
  Spray guns to which fluid pressure are applied, such as the ST-6PR, HM-1W and others, cannot be used with gravity containers as pressure is insufficient. Please use a pressure-feeding tank instead.
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Liquid leaks from spray gun
Nozzle and needle wear
  If the spray gun has recently been leaking liquid although it had been working fine before, either nozzle and needle wear or dust, as explained next, could be the problem.
Replace any damaged parts. Also, replace the nozzle and needle together. (The fact that the nozzle is worn means that it is highly likely that the needle is also worn.)
Dust or other foreign matter has adhered to the end of the nozzle
  Remove the nozzle and clean it.
When removing the nozzle, make sure to use the wrench that has been specially made for this purpose (for the ST and PR series). Use of a monkey wrench or pliers will damage the nozzle, rendering it unusable.
Two-way solenoid valves are being used for switching to piston air for models with piston air separation (ST-6, PR-30, etc.)
  Make sure to use three-way solenoid valves for air for piston operation.
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User suffers intermittent spraying
Nozzle loosening
  If the nozzle has loosened and the part that connects to the main body is damaged, air will penetrate the side for liquids, and the spraying will keep being interrupted. Replace damaged parts. If the nozzle is loose, use the wrench specially made for it to tighten it firmly.
Needle O-ring damage
  If the O-ring used on the part of needle or piston valve that separates liquid and air is damaged, air will penetrate the liquid side and intermittent spraying could result. Replacing damaged O-rings will rectify the problem.
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Mist drifts upward
  This is not an actual defect, but if mist drifts upward, it is because air pressure is high, which enables the mist to be emitted strongly. In addition, high air pressure will make mist particles finer. The fact that mist itself is fine means that the finish of paint and the like will be attractive, which in itself is certainly not a bad thing.
However, coating efficiency will be reduced, and for such usage purposes as applying press oil, mist will scatter around the entire workplace, deteriorating the work environment.
To avoid this, please select a spray gun that is able to work at low pressure: 0.1MPa or lower.
Possible candidates with systems that separate air for piston operation include the ST-6 series, PR-30 and HM-6. In addition to systems that separate air for piston operation, the ST-5P and other models are equipped with a built-in mechanism for achieving low-pressure atomization.