Air compressor switch for pump driven centrifuge??

[AcIdBuRn02ZTS]

Pressure safety switch for pump driven centrifuge...

Hey guys..

Been tossing around an idea... trying to figure out a safe way I can keep my centrifuge running while I'm away from the shop for long periods of time (such as at work)

I started looking around for pressure switches that I could plumb inline on the pressure side... something that could kill the pump if pressure spiked over 100psi or dropped below 70 or so (clogged regulator or line failure)...

The first thing that came up was a pressure switch for an air compressor... 70psi on.. 100psi off.. adjustable and capable of handling the load of the motor.

Now... will the switch itself hold up to oil use since it was designed for air pressure? If no, is there anyway I could isolate the switch but still have it see pressure... but not have oil in contact with the switch itself?

Thoughts?

Thanks guys
-Chris

 

[AcIdBuRn02ZTS]

Scratch that idea... I need low pressure off and high pressure off...

I'm looking at some other options but most of it is over my head. Basically looking for a switch that will be open below 80psi.. Then open above 100psi.

If I could find two switches that are rated for 125v and the amperage draw of the motor... It would be simple.

Series the two switches... One normally open with a setpoint of 80psi... One normally closed with a set point of 100psi...

Anybody have any leads on this?

 

[AcIdBuRn02ZTS]

So... here is the plan after a good bit of reading...

I'm hunting down some used switches...

Planning on running 2 100psi Ashcroft industrial pressure switches... One will be set at 80psi and wired to the N/O contacts on the swtich... the other will be set at 95-100psi and be wired to the N/C contacts... Power from the motor will be wired through both switches in series. So, once pressure is above 80 psi, switch 1 closes... and as long as it stays below 100 psi, switch 2 stays closed.

During startup, I will have a standard switch (light switch) that when turned on, will bypass the pressure switches. Once pressure is established, flip that switch off and the pressure switches take over. If pressure drops below 80psi, the pump motor will shut down (incase of line failure). If pressure rises above 100 psi (regulator clog, etc..) pump will automatically shut down. The motor I'm using is also thermally protected.

With this setup, one could leave the system running around the clock without much worry.

Thoughts?

I'm seeing these switches used on ebay for $20-30 each so cost wouldn't be bad... just a couple plumbing T fittings and it should be good to go.

-Chris

EDIT..

I may simplify this even further... just run 1 switch and a 100psi pressure relief valve plumbed back to the tank. Hmm... more reading to do.

 

[Brad S.]

Not a 100% sure on this comment, but the PA biodiesel CF I use, needs wmo to function correctly....
I'm guessing you'd have to get one for compressed air use only..???
Just thinking out loud..

 

[AcIdBuRn02ZTS]

.... The pressure switches will just be "T"ed into the high pressure supply to the 'fuge... If pressure drops or goes too high, it shuts off power to the pump until it is reset.

This won't block or control oil flow in anyway. The power supply leads to the pump motor are ran through the two switches. As long as the pressure stays between 80-100psi, power stays on. If pressure goes out of this range, power to the motor is shut off until it is manually reset.

 

[Brad S.]

oh ok, my bad, i was thinking totally run by air pressure, but your talking about pushing the wmo with compressed air to the CF. Gotcha..
That sounds like how some oil burning stove/furnaces are fed by compressed air.

 

[AcIdBuRn02ZTS]

....lol

No.. I'm talking about a gear pump driven centrifuge such as the pa biodiesel unit...

Motor turns a powersteering pump which drives the centrifuge. The pressure switches would shut off the pump motor when pressure spikes or drops... just a safety feature for running the 'fuge when away from the shop...

Make sense?

 

[A48WillyzGuy]

Brad, the only reason compressed air was mentioned was to suggest using one of the switches normally found on an air compressor to stop the CF pump motor rather than an air compressor motor. Does that help?

I think the two switch idea is pretty good. It would be better than just letting the motor run all day, with the fuge bypassed, in the event of a clog IMO.
Though, I guess that depends on where the bypass is. If it's in front of the low pressure switch, it should drop pressure enough to trip the switch. Yay for thinking in text. Lol

 

[AcIdBuRn02ZTS]

^
Yup..

The air compressor pressure switch was just a hairbrained idea that wasn't thought through. I got a pressure switch coming my way though... an Ashcroft B420B ($29 shipped to my door used but working). Its a 100psi pressure switch that is fully adjustable.. has both "Normally Open" and "Normally Closed" contacts... has a nitrile diaphragm which is replaceable... and has a 15 amp rating. Same switch new is over $200 depending on where you look.

We will hopefully be relocating the system soon and get it all setup with this switch and a pressure pop-off valve that will be plumbed back into the main drum. The switch will be set to shut the pump motor off at anything below 80psi and the pressure relief valve will open at 100psi. Should make for a reliable setup that can be ran throughout the day without much risk.

-Chris

 

[Brad S.]

Thanks for the free education guys.
The point you bring up about "leaving stuff running while a person is gone" is a important.
I've got a 15 gal plastic drum that I use when I'm CFing and I figure that takes less time for me to process.
I really don't trust leaving stuff like that running while I'm gone.
Plus when i refill my wmo tank(about 20 gal total, 15-17 gallons useable) on the pickup it fills it.
In the big scheme of things I'm probably running my whole system more BUT at least I won't "repaint" the inside of my garage in "flat black wmo"
But I really like hearing what everyone else is doing, gives good ideas for future improvements.

 

[AcIdBuRn02ZTS]

1 of the new switches came in...

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Looking forward to setting it up. Should be pretty simple... Npt port on bottom.. NC and NO contacts and a single but to adjust pressure. Hopefully we'll see how it works soon.

 

[The FNG]

Hope the project is working out for you! Did you get the switch installed? I would set the second one for a lower PSI. I believe the pressure driven centrifuges are rated to work all the way down to 40PSI.

 

[AcIdBuRn02ZTS]

Not installed yet.. In the process of moving and will be relocating the oil rig soon... Then the revamp.

Theory behind setting the 2nd switch at 75-80 would be for any loss in pressure such as a small leak would trip the switch. If its set to 40psi, it would have to blow the line or drain the drum before it would shut down I would think...