Tuning Drilling Regulator inlet port.

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superchikn

superchikn

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Oct 8, 2019
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Schwenksville, PA United States
So, I was working with my buddy on his new PP750, porting etc.
I had seen in a video or read that the regulator feet port from the cylinder is so small that it takes 20 to 30 seconds for the (small plenum to refill between shots. I removed the adjuster screw and drilled the tiny wire drill size out with a drill about 30-40% bigger in diameter.

In retrospect I realize this is not something I have seen talked about much if at all. The reason I questioned doing that is that his ES went to crap, in fact the gun was acting unregulated with a steadily climbing shot string. I finally got him to take it apart yesterday and he found the large (main) reg. oring torn up and with tiny brass chips embedded in it. Obviously the reg was not cleaned thoroughly enough after reinstallation.
The oring was replaced and the drill site cleaned again of chips and reinstalled. Better but still a mess. I suspect there are chips in the spring stack.

At any rate, is it bad practice to increase the size of the port which feeds the regulator from the tube or tank?
 
Privateer said:
So..... You drilled the reg but it was never disassembled when you did, correct?
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Hey Jeff,
No, I removed the adjuster screw completely and left the rest of the reg on the kitchen table, far away from the drill press. I believe that when I asked him to clean the chips out of the piece I drilled he was not thorough. Other than a visual inspection of the belleville configuration and for cleanliness the rest was not touched.
 
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Couple pictures, courtesy of Thane from his thread, if you are not familiar with the reg. of this gun.
I drilled the hole in the first pic on left, what you see is an oversized hole, there is a much smaller one at the bottom of that opening.
In the third pic you can see the adjuster laying above the reg. spool.

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Privateer said:
Ok. Then I'd think there's chips/very fine particles still in there somewhere.
Maybe even damaged belleville washers?

No idea on if drilling it would help recovery time myself.
But 20 to 30 seconds recovery time sounds obscene to me!
Click to expand...
I'm sure there are still chips, I will have to go over it as soon as I can get it from him.

20 to 30 seconds is obscene. I did not measure the recovery time it but with the tiny plenum I believed what I read. Didn't think it could hurt.

I have the extended plenum/gauge block and I do not notice it on my gun as I think I am not dumping the plenum on every shot.
 
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Despite lots of unknowns, I would be shocked if the slow recovery is in any way the fault of the orifice size. Most regs have a very small orifice yet have no trouble replenishing a plenum quickly...even at fpe levels (read: air consumption) much higher than a PP750, and even with a flow restrictor screw installed as in the case of Huma regulators.

More likely the cause is wear and/or a poor fit at the valve seat. What happens is the seat quickly reaches an almost closed state but air continues to eek through microscopic voids over a long period of time until the pressure finally climbs high enough to totally squeeze it closed.

Inspect both mating surfaces of the valve seat with the aid of magnification. If the plastic part is dented badly or has little wispy plastic fibers in and around the indentation, it needs to be either replaced or wet sanded flat and smooth. If the other surface, usually a raised cone, has machining marks or a burr, carefully dress it as well. Meaning just the truncated end of the cone...the part that meets to the plastic seal.
 
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Regarding the purpose of the atmospheric vent, it helps first to understand the fundamental way a regulator works. The regulator's piston has a large end and a small end. A given air pressure therefore exerts a small force on one end and a larger opposing force on the other end. The elevated force on the large end serves to compress a spring (whether a conventional coiled spring or Belleville disc spring), such that when the pressure reaches the desired setpoint, the piston has moved sufficiently to squeeze the valve seat closed and halt the transfer of air from the reservoir to the plenum.

So here's where the atmospheric vent comes into play....

If the chamber containing the spring were instead sealed, it would gradually become pressurized by way of gas permeation through the O-rings. It's a real thing. When that happens, the opposing forces between the two ends of the piston are thrown out of balance and the regulator's setpoint begins to migrate downward. A vent ensures this condition does not arise.

Some regulators don't require a vent hole in the tube, and instead employ a clever way of venting through the threads of an end cap or something of that nature. But any properly designed regulator has a venting feature of some kind to avoid the problem.

[edited to correct upward to downward]
 
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Thanks Jason,
I can't take all the credit though. I have not seen the gun in almost two weeks. He has been cleaning the reg, changing o rings and adjusting reg setting and HS since initial reassembly to get back to a good shot string since the power mods.
More work to go and then the fine tuning.
This was his first time inside an airgun so it has been fun for both of us.
 
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