Compressor questions

[Jimmer]

I've sort of got this thing for compressors, but so far all the compressors I've owned and built have been 125 - 200 PSI shop compressors, so I have some questions about our compressors. First off with a fully automated compressor with auto drains and a pressure switch, is it the pressure switch that dumps the pressure from the block when it reaches pressure, the way my shop compressors do, or do the auto drains open when the compressor shuts down?

The other one that popped into mind was plumbing. If I was to build a system for continuous blending, would it be advised to make all the fittings SS or Brass, or would I be ok using plated fittings for hydraulic use, provided that they are properly cleaned?

Thanks,
Jim

 

[pescador775]

Plated fittings OK for CB. Use a real oxygen reg for the O2 tank.
These guys can answer some of your questions including some circuit diagrams for auto drains, etc.
Compressor_Team : Compressor

 

[cool_hardware52]

I've sort of got this thing for compressors, but so far all the compressors I've owned and built have been 125 - 200 PSI shop compressors, so I have some questions about our compressors. First off with a fully automated compressor with auto drains and a pressure switch, is it the pressure switch that dumps the pressure from the block when it reaches pressure, the way my shop compressors do, or do the auto drains open when the compressor shuts down?

The other one that popped into mind was plumbing. If I was to build a system for continuous blending, would it be advised to make all the fittings SS or Brass, or would I be ok using plated fittings for hydraulic use, provided that they are properly cleaned?

Thanks,
Jim

Shop air compressors use a bleed down or unloader valve to release pressure from the cylinders at shutdown to reduce the starting load when the pressure switch turn the motor on again. A check valve at the receiver keeps the compressor tank from emptying through the bleed valve.

Auto drains on breathing air compressors are usually air actuated, normally open valves that use interstage pressure to close the drain.

A timer and electrical solenoid will vent this pressure after a period usually set with a TDR or Time delay Relay, a second TDR will control how long the drains stay open.

This solenoid will also usually fire when the main pressure switch shuts down the motor. This not only drains the compressor, but bleeds off the pressure in the cylinders to allow for restarting.

In addition because the drain valves are normally open, they will be open at startup, until the interstage pressure build to a point sufficient to close the drain valves.

You want to limit the flow through the drain valves, if unrestricted you may never build enough interstage pressure to close the drains at startup.

These guys make the valves Aqua Environment Parts List by Function

You need one drain valve for each point on the compressor you wan to drain, i.e. if you wan to drain two interstage separators and one filter tower you need three valves.

You can run all the drain valves via one common electrical solenoid.

Tobin

 

[pescador775]

OK, since we're getting into this here I feel obliged to mention that some military compressors use a dump valve controlled by oil pressure. When oil pressure drops the coalescer bleeds (blasts) down. There are a number of variations on this with timers and other controls which the compressor group have been discussing using diagrams, drawings, pictures and sources . Peter and Jim are the go to guys for circuitry. Some interesting air pressure operated drain valves are fitted to the SW compressor at auction on EBay right now.

 

[oxyhacker]

Depends where you are going to use them. Normally, in a CB system, you decant the O2 to near-ambient, right at the regulator, which is at the tank. So as long as the regulator is OK for O2 there's no problem. But if you are planning on some more elaborate system, where the O2 is runs though valves, pipes or tubing, either to cascade your O2 bottles or take the O2 to a panel, them steel won't do. The rule of thumb being that HP O2 should not come in contact with any metal but brass, bronze or SS.
For the output side of the compressor, steel hydraulic fittings are usually OK for any mix you are likely to be putting through a compessor, but do note that many hydraulic valves, check valves especially, are not bubble tight when used with air.

The other one that popped into mind was plumbing. If I was to build a system for continuous blending, would it be advised to make all the fittings SS or Brass, or would I be ok using plated fittings for hydraulic use, provided that they are properly cleaned?

Thanks,
Jim

 

[fppf]

Personally I would use all SS fittings.
They cost more but you don't need to worry about rust or contamination. Hydraulic fittings are made to run oil through them, not soaking wet air (before coll. and filters).

 

[pescador775]

I use brass and stainless for oxygen.

I have a 34 year old Capitano and it has installed plated steel fittings. No problems.

I use stainless on my home made compressors in keeping with their military/aircraft origins. Well, there is one 45 deg elbow that is plated. I ran out of surplus, military elbows and declined to pay 15 dollars for one at McMaster Carr.

Either way but, as Hacker said, plated steel not recommended for HP oxygen.

 

[Jimmer]

Depends where you are going to use them. Normally, in a CB system, you decant the O2 to near-ambient, right at the regulator, which is at the tank. So as long as the regulator is OK for O2 there's no problem. But if you are planning on some more elaborate system, where the O2 is runs though valves, pipes or tubing, either to cascade your O2 bottles or take the O2 to a panel, them steel won't do. The rule of thumb being that HP O2 should not come in contact with any metal but brass, bronze or SS.
For the output side of the compressor, steel hydraulic fittings are usually OK for any mix you are likely to be putting through a compessor, but do note that many hydraulic valves, check valves especially, are not bubble tight when used with air.

Yeah, I suppose I should have clarified that I meant strictly within the compressor and downstream of the compressor. Upstream in the O2 supply circuit I had intended to use nothing but brass. Also I was only thinking things like elbows, tees, etc. anything like a check valve or pressure maintaining valve would be specific for HP air, not a hydraulic part.

 

[cool_hardware52]

OK, since we're getting into this here I feel obliged to mention that some military compressors use a dump valve controlled by oil pressure.

That's also pretty common on larger piston type shop air compressors. I have a 20 hp Worthington with a similar bleed down system.

Tobin

 

[pp-1-3-5-7-9]

I've sort of got this thing for compressors, but so far all the compressors I've owned and built have been 125 - 200 PSI shop compressors, so I have some questions about our compressors. First off with a fully automated compressor with auto drains and a pressure switch, is it the pressure switch that dumps the pressure from the block when it reaches pressure, the way my shop compressors do, or do the auto drains open when the compressor shuts down?

Thanks,
Jim

Normally the auto stop switch which installed on the shop compressors have combined with a unload valve, when the tank pressure reached to the set pressure the auto stop switch will trigger and cut off the power for the drive motor until the tank pressure dropped to a certain level the switch will reset and turn on the motor again, when the switch getting to rurn off it when the pressure reached to the set point, at the same time the working arm of the switch will also press the unload valve to release the pressure which remain in the section between the compressor discharge port to the check valve of the tank to help the compressor can be get a easy start up.

We are not call it as auto drain valve but just unload valve.