compressed air pressure problem

[Eveslage]

I hope somebody can help me with this. I have a little 1" Air operated diaphragm pump that only needs about 5CFM @ 50psi to operate. Our main air compressor makes about 540CFM @ 100psi. There is a hard lined 1” pipe off of our 2” header line that originally fed the pump, but that didn’t get the pump enough air. So the engineer before me ran a 1” hose about 100ft. from the header right next to the compressor. So there is a T in the 2” header. One way goes on and the side has bushings down to 1” then another 1” T with the hose coming out of the side running to our pump. The main compressor can only maintain about 80-90psi by itself so we have a portable compressor that makes about 350CFM for backup. The 2 together still have a hard time getting to 100psi. We need about 90-100psi at the compressor to make the pump work.

So here is my question. Can the 540+CFM of air going through a 2” pipe be moving so fast that it can’t really make the turn to go into the side of the T and it just blows straight through to the rest of the system? Therefore leaving the 1” hose at substantially less than 90psi, more like 30-40.

Thanks for the help
Eric

 

[NickE]

In a word NO. In a pneumatic system the medium is available at all taps.

I want to know why,if your diaphragm pump only needs 5scfm@50psi, the main compressor does not make it run.

Seems to me that you have a problem with the piping. or the pump needs much more air than you think.

On one hand you say the pump only needs 5cfm@50psi.

then you say your main compressor can move 540+cfm@100psi.

Then yoy say the backup compressor can move 350cfm@(guess80-90psi?)

To me that says that your delivery is ~900cfm@~80psi(min)....

Which should easily run your 5cfm@50psi pump.

 

[Eveslage]

Everything you stated is correct and that is my problem. The hose is open and we should have lenty of air. There are many other air operated pumps in the plant that are consuming air, but the hose to the problem pump branches off very close to the compressor. According to the pump curves 5CFM should make the pump run.

 

[NickE]

What is the total CFM that your devices can use simeltaneously?

if that # is greater than 900CFM it doesnt matter how big of a line feeds the device, there wont always be enough air to run everything.

(Right, a pneumatic system only shows a gauge pressure when the supply cfm is greater than the demand (load) cfm. If load cfm shoots up then pressure shoots down, until the compressors can deliver enoguh air to fill the system back up. Or until the load drops causing pressure to increase.)

I dont know how well you know about basic electrical concepts, but thats how I envision it....

Volts == pressure
Amps == cfm.

If you increase the current draw on a circut, then there is a voltage sag in the supply. Unless the system has enough overcapacity to supply the high current demand for its duration. i see this all the time with professional sound system amplifiers run off small circuts. Ive even seen 12vac lamps dim during heavy bass hits. (ie: the voltage sag in the mains is severe)



Nick
I love materials science!

 

[zdas04]

Have you stuck a gauge on the line right before the pump? Your pressure drop in 100 ft of hose could exceed the dP you have available (i.e., 100 psig at the compressor minus 50 psig minimum to operate the pump).

Does the pump exhaust locally or is it piped outside? If it is piped outside, check for bugs in the exhaust outlet, plugging often creates more backpressure than the compressor can handle. I line to put a needle valve on both the inlet and outlet very close to the pump to stick in gauges to measure actual dP.

David

 

[NickE]

zdas- thanks, that is going to come in real handy on a project I'm developing here at work, I totally missed using dP. (eh... I'm a metallurgist not an industrial)



Nick
I love materials science!