Building a compressor...

[4684]

Firstly hello to everyone on here, I've come here to make sure I do things properly

I've started to build a bigger compressor, before this weekend I had a three phase 3hp, 14cfm, 150l compressor going

I now have another 14cfm pump and 3hp single phase motor mounted up on the tank, bolted down and lined up

I've made a start to plumbing in the 2nd pump feed, having put a t-piece in existing pump feed before it gets too the tank, just needs some 15mm copper pipe bending up abit now and thats done.

The question I've got is though, I need to add another presure switch to control the other motor (the 2nd motors single phase)... Does the second switch have to have both conections like the other one, or can I get away with just t-ing off the plastic tube thats there, and feeding the 2nd switch with just the small presure take off? Can a presure switch work like this, or does it need another blowoff/take off point below it as well.

Theres not another conection on the cylinder, so I would proberly end up removing the current presure switch mount/valve/feed, that the switch sits on, and doubleing the hole up with plumbing fittings producing two points from one if that makes sense!? spacing it apart with pipe then having both switches stud together.

thanks for looking!

 

[rtbcomp]

I think you've got wrong.

If you T two pumps into the same delivery pipe you could arrive at the situation where one pump is running and the other needs to start. No 2 pump will have to start against the pressure from #1 pump, and it probably won't.

Conversely one pump could have cut out and opened the unloading valve, which means the 2nd pump will be feeding to fresh air and never cut out.

The way you should do it is to have each pump with its own delivery pipe, non-return valve and pressure switch.

Welcome to the forum by the way!

 

[4684]

Right I see...

Eeeek gonner have to drill two holes in the tank then and weld some male iorns in...

one for another pump feed, and I'll need the fittings to supply the air feed from this as well, to the presure switch, and another hole for the extra presure switches conection below it...

Basicly I've gotta run the two totally seperate all together and not double up on any holes, fittings what so ever.

Also the non return valves on each pump feed...

right ok, nice one for the help fella! and cheers for the welcome

Edit: Everyones more than welcome to laugh at my paint drawings

(how it used to be)

(how it was going to be)

(how it should be)

the pump feeds were going to piggy back in that arrangment as well, single phase tapped to the old 3 phase supply. all conections where going to made in the location their pictured as. I odv can't use one presure switch because one of my motors in single the other is three phase.

 

[tigler]

It will work with each delivery pipe having it's own non-return valve to the receiver, but the pressure sense feed from each non-return valve can be fed via a one way valve, tee'd together and into one pressure switch. This is how commercially made tandem compressors are configured.

 

[rtbcomp]

..... but the pressure sense feed from each non-return valve can be fed via a one way valve, tee'd together and into one pressure switch. This is how commercially made tandem compressors are configured.

No no no

The so called "pressure sense feed" is NOT a pressure sense feed, it is the unloader pipe from the NRV to the pressure switch, each compressor must have its own.

The pressure is fed into the switch from underneath. Have a look in my albums under air compressors for some diagrams.

 

[rtbcomp]

You shouldn't have to drilling the tank. You can take a T off the existing pressure switch, there are usually 3 or 4 ports on these, there's bound to be a spare, or remove the safety valve, T in the 2nd switch and re-fit the safety valve to that.

The NRV will have to be connected straight to the tank, but you can always use a T-piece into an existing port.

 

[tigler]

No no no

The so called "pressure sense feed" is NOT a pressure sense feed, it is the unloader pipe from the NRV to the pressure switch, each compressor must have its own.

The pressure is fed into the switch from underneath. Have a look in my albums under air compressors for some diagrams.

Sorry, I meant unloader line. They can be tee'd together if they both have a one way valve. I've seen loads of tandem compressors plumbed that way.

 

[rtbcomp]

The unloaders have to be kept separate, One from NRV #1 to Pressure Switch #1 and one from NRV #2 to Pressure Switch #2. I don't see how connecting them together can work.

 

[tigler]

I've very definitely seen it done that way on numerous tandem compressors. I don't see the problem, 1 pressure switch turns off both pumps and they unload through one way valves tee'd together to the pressure switch.

 

[rtbcomp]

Yes doing it that way I see what you mean. The compressors I've seen have a switch for each pump so they can switch off at different pressures to avoid mains surges, more important in a domestic setting.

The advantage of doing it your way is that both pumps get a chance of a rest, doing it my way there is a possibility that the pump with higher pressure setting will run all the time.

 

[4684]

Nice one guys for your help

and rtbcomp your diagrams were spot on

I know what I'm doing now... it all makes sense

Need to get this built so I can get the blast pot powerd and get the Capri blasted at last!

I meant to ask as well, its pointless starting another thread...

I wanna make sure both my pumps are good before I finish this thing, I asume you can change the piston rings on a pump and the odd gasket in places, is there anything else you can do to them? Is there a test I can do to them, possibly ruel out the need to open them up, maby like compression testing an engine? I guess if I locked the pump and stopped it from turning, then pushed air back up threw the pump up to say... 100psi then looked to see how long it held its presure for, that could tell me if the rings/gaskets are good, but it dont tell me how much CFM/air the pump produces. I want to be sure they make 14cfm each, so I'm not wasting my time and I'm producing the 28cfm im aiming for

 

[tigler]

Generally, if the pumps have had the oil changed regularly, and the airfilter cleaned or replaced, the thing that really determines performance is the valves. On most compressors now they are stainless steel reed valves which either work or not, if they don't then they are just replaced which is simple to do.
Worn piston rings or bores will reveal themselves by excessive oil in the outlet pipe.

 

[4684]

Right, ok I'll proberly just give them new air filters and an oil change then.

they dont produce any funny noises or loss of fluid or anything...

One a ABAC pump and the others from a Easyair compressor I think their the makes. Ones blue the others dark grey with red and silver sticker, I'm working from memory though as their down the workshop

Edit:

yeh just looked ABAC is a make, so thats one, but easyair dont seem to be a maker... it must be the model of it. I'll have to have a look, both are very old now and I've not owned either of them from new, they could of gone through alot of owners for all I know.

As said though neither make any untoward noises, when you turn both with your finger over the end no oil comes out and its too hard to hold your finger on after 2 rotations.

 

[tigler]

If they don't take a prolonged time to build pressure then they are probably ok. If valves fail they either won't build pressure or take ages to reach a much lower than normal pressure.
If you listen carefully when it's running, the valves can be heard ticking slightly.

 

[4684]

Gooood stuff, when I first set out todo this I was gonner use a Honda GX160 engine (5.5hp) petrol engine and power the both of them from the engine, but the electric start bracket/motor for those honda gx engines are biiiiiig money

I brifely considerd a small four stroke engine like a 125 or w/e, but its the starting stopping I cant be botherd with.

 

[tigler]

bang some images up when you can, it's always good to see each others projects.

 

[4684]

Will do, been looking for somewhere about compressors for ages, I've had the car in sanded bare metal for munths now needing to be blasted and not had the compressor big enough to power...

http://www.ebay.co.uk/itm/Bead-Shot...666?pt=LH_DefaultDomain_3&hash=item3cb70c26da

28CFM should be ok if thats how it works 14cfm pump x2 produces 28...

 

[@Turbo]

that looks like the one I have about i found it quite difficult to get the ceramic nozzles. and make sure to keep the air dry it clogs at the bottom if you dont.

not a bad rig tho.

 

[brightspark]

that looks like the one I have about i found it quite difficult to get the ceramic nozzles. and make sure to keep the air dry it clogs at the bottom if you dont.

not a bad rig tho.

change the nozzle to a 3mm carbide one and bin the ball valve on the end .regulate of the input feed valve

 

[@Turbo]

change the nozzle to a 3mm carbide one and bin the ball valve on the end .regulate of the input feed valve

sounds more like the thing cheers