Pressure on the Priority Valve????

[oxyhacker]

We were talking about priority valves at the Bauer workshop at DEMA.

One thing they pointed out, that I'd never really thought about before, is that a Bauer (or other compressor with a floating HP stage piston) MUST have a functioning priority/constant backpressure valve to operate correctly because the floating piston needs a certain amount of pressure on it to keep it from hammering itself to death. This is why Bauer compressors have always had integrated BP valves, long before other manufacturers started fitting them (if they fit them at all). If the floating piston goes on hammering longer than usual, the backpressure valve is usually the culprit.

This also means that if you are fitting a large amount of extra filtration to a compressor with a floating piston that it is important to leave the original BP valve in place, and put an additional one on the output of the extra stack(s). If you just move the orignal one to the output end of the extra stacks, then the floating piston will go on knocking until all the housings are pressurized, which can damage it.

 

[pescador775]

Bauer (Mako) did not supply backpressure valves as standard equipment until the late 70's. It does not take much backpressure for the third stage to operate correctly. Before BP valves, it was customary to leave the tank valve shut until the beating noise stopped. I have never personally seen any damage done as a result of the third stage free piston. Not saying it doesn't happen but...., Bauer compressor manuals of the time described the noise as "irrelevant".

Where did "priority" valve come from? A priority valve is a multi-outlet device which assigns individual flows based on the "priority" which is dialed in at the time. I smell a dive industry "agency".

 

[rjack321]

Richard,

The pressure gauge on LF (3rd chamber) is located on the right before the priority valve. I have a whip guage on the hose to the tank...

So, I can compare the pressure before and after the final priority valve.

But, it is identical. That's my question. Why?

The 2nd valve may very well be stuck open. Do you have a picture?

 

[pescador775]

About floating pistons:

The Kidde four stage employs three floating pistons which are driven by cams as opposed to the Bauer design where a crank is driving a piston rod. The Kidde pistons, unlike the Bauer third stage, are not subject to free floating out of synch with the cams and so no banging noise is produced. This effect is avoided by generating back pressure within the cylinders themselves, not in the air line. Back pressure is produced by means of flow restriction. For example, the fourth stage exhaust passage of the Kidde is the diameter of a #68 drill, about the size of a cat whisker. At the Kidde's very high rotational speed, air is not fully evacuated (reach equilibrium) from the cylinders until several hundred psi head press is reached which occurs in a fraction of a second. Thus, back pressure at the piston heads puts the pistons in contact with the cams immediately after start up.

 

[Hoosier]

As I believe, I have three priority valves.

Compressor (mine is Alkin AD model, not plain one so it comes with a BP valve as I was told).
2nd chamber
HF appliance



Here is the link that you can see my chamber. Mine is an absolute portable design.


The warranty is still effective on LF HF appliance, so I might contact LF for the warranty service after getting you guys feedbacks.

 

[pescador775]

Hoosier, the only suggestion I can come up with is to adjust the BP valve located on the LF 3rd chamber distribution block while the compressor is running and the fill manifold is wide open to flow. Start with a minor adjustment and check the pressure gauge at the same location.

 

[rjack321]

Once the last valve opens on the HF appliance it is staying open. I don't exactly know why. I am guessing that the valve is designed for a much larger compressor. So the passages are sized so large that it effectively drains your HF chamber when it opens. They do tend to leak after their first opening and the leak rate on this valve is approximately the same rate as your Alkins. I would ask LF what its capacity is and why its not working at 3.5 cfm. You may need to swap it with the first priority valve (which is hopefully smaller).

On a side note, I think you have too much filtration for your little 3.5 cfm Alkins unit. You are getting to the end of the useful cartridge shelf life (6-12 months) way before you could possibly pump enough gas to use up those huge (expensive!) filters.

I would remove the intermediate priority valve, which I'm guessing is the one in the upper left on pic 1, you don't need it. You may need it to replace the oversized backpressure valve #2 though.

 

[pescador775]

If the third chamber back pressure valve is leaking more than 0.1 cfm it is defective. I suspect that the valve's internal piston is sticking. Changing the spring tension on the piston might give an indication of this if the gauge pressure at the distribution block suddenly rose during the adjustment procedure.

Otherwise, I would suspect that the gauge is somehow reading downstream pressure but the fact is that the gauge demonstrates that the valve works on startup, but not during constant flow.

 

[Hoosier]

Hoosier, the only suggestion I can come up with is to adjust the BP valve located on the LF 3rd chamber distribution block while the compressor is running and the fill manifold is wide open to flow. Start with a minor adjustment and check the pressure gauge at the same location.

Done that.. I could adjust the pressure point with the gauge. 2,200 psi, 2,000 psi, or 1,800 psi....

Once the last valve opens on the HF appliance it is staying open. I don't exactly know why. I am guessing that the valve is designed for a much larger compressor. So the passages are sized so large that it effectively drains your HF chamber when it opens. They do tend to leak after their first opening and the leak rate on this valve is approximately the same rate as your Alkins. I would ask LF what its capacity is and why its not working at 3.5 cfm. You may need to swap it with the first priority valve (which is hopefully smaller).

OK... I will try to get some answers from LF.

Question: When I set up the breaking pressure on Priority valves, 2nd priority valve must be lower than the final priority valve on HF appliance?

On a side note, I think you have too much filtration for your little 3.5 cfm Alkins unit. You are getting to the end of the useful cartridge shelf life (6-12 months) way before you could possibly pump enough gas to use up those huge (expensive!) filters.

I would remove the intermediate priority valve, which I'm guessing is the one in the upper left on pic 1, you don't need it. You may need it to replace the oversized backpressure valve #2 though.

Agree. As I post on other thread, "2nd chamber challenge" I would like to make each chamber totally independent because all air doesn't need to be through HF appliance, but I did mostly.. Second, as you see, I used a lot of QD, so I can move any chamber without draining all airs...

Yes, the capacity of 2nd chamber will be overkill, but I thought it might be able to extend HF filter life ($160 each) and my 32" chamber is re packable canister inside, so it doesn't cost that much (I think).

If the third chamber back pressure valve is leaking more than 0.1 cfm it is defective. I suspect that the valve's internal piston is sticking. Changing the spring tension on the piston might give an indication of this if the gauge pressure at the distribution block suddenly rose during the adjustment procedure. .

It is beyond my area. How can I figure out 0.1 cfm as a regular Joe home mixer?

Otherwise, I would suspect that the gauge is somehow reading downstream pressure but the fact is that the gauge demonstrates that the valve works on startup, but not during constant flow.

I should ask this to LF....

 

[rjack321]

I would try adjusting the spring tension too. Mine worked fine for the first couple hours I owned it then loosened up by over 1000psi. Been steady at 2000psi ever since (150 hours use). I guess the spring broke in. Might have happened here.

Or he could swap it with priority valve #1 and see if that one holds pressure.

Plenty of parts to play with and deduce the source of the problem.