Tandem compressor project...

[esc]

Hello all,

I was hoping if I stuck this on here I could get some advise as I'm going along, it would be fantastic!

Ive decided to build my own tandem setup compressor, powerd by an engine. It seems the best solution for the intended use as a mobile compressor in a van, and £ at the moment.

I've already got two 14CFM (min 3hp) pumps, one from a non working compressor (motor went) and one from my 3phase compressor.

I cant afford a new single pump, that puts out the CFM I'm after at the moment so I've decided I'm going to recondiction these two and combine them.

I've got a 150L tank already stripped, just needs paint, that I can use. I did want something smaller and was going to use a 47kg tank, along with one pump (for size reasons in a van) but budjet budjet. Also I ended up thinking it was going to be too much hassel welding in the fittings to the 47kg tank as it would have been a calor gas one.

I've started by cleaning up and taking apart the pump from the non working compressor to get an idea for whats envolved... I cant beleive how simple these things are though once you get them open.

from this doing this I now see I'm going to need the following...

deglaze cylinder using...

and new piston rings, making sure I dont have anymore than a 6thou gap around the crown of the piston when its back in the cylinder.

new gaskets and valves.

This brings three questions... One pump is from a ABAC compressor and the other a COMPAIR both almost identical to each other. I havent opend the second yet so dont know if its the same sizes, but does anyone know anywhere on the net I can order the right replacment valves/gaskets and rings from?

The valves are on a flat plate, and the valves them selfs are no more than thin metal tabs with small pins holding them flat on the plate, I've looked and looked for a picture to demonstraight but cant find one. Can only find pictures of big black plastic round ones than sit in a flat plate.

The other question is, do I have to replace the big end rod shells and bolts If I undo them to get the pistons/rods out?

Last but not least, Does anyone know the correct torque setting for the big end rods to the crank, and top and bottom bolts for the head? Also is there a tightening order?

I wasnt going to worrie about replacing the crank main bearing ball races?

The pump is exstally like this if it helps...

Many thanks for reading!

 

[tigler]

Ignoring your initial questions for now, have you established the correct running speed for both pumps ? If they're different it could be a problem. Also, what is your plan for controlling the cut in and cut out pressure ? It either needs to be a clutch that disconnects drive from the engine when the cut out pressure has been reached, so that the engine doesn't have to stop and start, or, an unloader valve that vents the oultet from both pumps to atmosphere when cutout is reached and closes to again when cut in is reached, so that the engine can run continuously.

 

[esc]

This is why I came here

How do I determain the pumps optimum speeds? Working out the size of the two pullys on the engine, and the pullys on the pumps was something I was going to ask later. I should be able to work out what RPM the engines doing at what throttle though easy enough. I guess the thing to do is see if there is an RPM rating on my two motors that powerd the pumps to begin with?

I'm glad youv bought the starting/stopping up as it was something I was working upto.

I've got a circuit in mind that when the presure switch comes on it starts the engine, by powering a timed relay to make the starter turn (relay would power the starter for about 5 seconds) then when the presure switch turns off the engine is killed, and turned back on ready to be cranked again. Is it a bad idea to start/stop it all the time then?

I thought you had to use unloader valves full stop. I plan to have both unloader tubes T into one and put it on the presure switch, will that be ok? I've got two check valves with the unloader tube conection on, I was going to stick a female T (centre male thread) in the tank and plumb them in like that.

 

[tigler]

If you know the motor speed of the original motors the pump speed can be calculated from the pulley ratio.
Commercial engine powered compressors run continuously with the unloader valve controlling pressure. Starting and stopping the engine is not a good plan, in intermittent use it would never reach operating temperature, and in continuous use it would need to start and stop very frequently, depending on air consumption.

 

[esc]

So I dont need to make a circuit then, just start the engine up when I want to use it. Easier I suppose, shame it has to run all the time though :P its just I cant afford an inverter and battery big enough to run a motor big enough to power two pumps. I'm going to need 6hp arent I?

Will the normal unloader setup be ok? Instead of a short hiss when the motor used to go off, that hiss will be constant? Gonner be abit loud isnt it :P

 

[tigler]

The non return valve into the receiver prevents air blowing back as the unloader opens, so there is just a chuff from the unloader exhaust from the pump on each stroke. A silencer can be used to reduce the noise on the unloader exhaust. So no electric circuit for a valve is required.
Some industrial compressors use the same method with electric motor powered units, I have one. This is to prevent frequent start surges overheating the motor as they have a limit to the number of starts per hour, and reduce energy consumption.

 

[esc]

Cheers for the advise its spot on, really useful because I'ed of just hit these problems along the way.

Is there a typical rpm for a 14cfm 3hp pump or can it vary alot? They all look pritty common with very little variation. I'm sure mine are exstally the same as the ones from machine mart?

 

[brightspark]

Is there a typical rpm for a 14cfm 3hp pump or can it vary alot?

they either run of a 1450rpm motor or a 2800 rpm

 

[tigler]

He means pump speed.
Yes, they do vary and it's quite important to run them at the correct speed as they are splash lubricated so speed affects lubrication.

 

[esc]

Dam, the chances of the two pumps turning at the same speed is looking pritty dull :P

 

[Shox Dr]

use different sized pulleys

 

[esc]

Going to do some investigation tomorrow and see if the motors have any rpm clues then. Can I work it out by measuring the pullys if its not on the motors? How would I meansure them, just the diameter?

If the pumps are 3hp minimum, does the engine want to be 6hp or abit more?

 

[brightspark]

Going to do some investigation tomorrow and see if the motors have any rpm clues then. Can I work it out by measuring the pullys if its not on the motors? How would I meansure them, just the diameter?

If the pumps are 3hp minimum, does the engine want to be 6hp or abit more?

generaly if theres a 3hp electric motor fitted petrol ones are 5hp

 

[esc]

Looks like it could be more like a 10/12 then?

The motor that came with the pump I've taken apart (ABAC) says "n/1' 2800" thats the only thing that looks like a RPM anyway...

and also "HP 3KW 2.2" so its not a 3hp after all... would that mean the pump is more likly to be a 12CFM one?

 

[eil]

Looks like it could be more like a 10/12 then?

The motor that came with the pump I've taken apart (ABAC) says "n/1' 2800" thats the only thing that looks like a RPM anyway...

and also "HP 3KW 2.2" so its not a 3hp after all... would that mean the pump is more likly to be a 12CFM one?

3HP is the same as 2.2KW.

 

[FranV8]

Yes, it's written the wrong way round - instead of 3hp 2.2kW, it's, presumable on the name plate, stamped up HP:3 kW: 2.2

You could back calculate the rpm, by working out the swept volume of the cylinders (pi X (cylinder diameter squared) X stroke, then see what RPM is needed for them to displace 14 cfm (which is what their volume flow will have been quoted as)

In reality, you get around 3cfm per hp for this type of compressor (that's FAD, i.e the actual air you get out of it)

 

[esc]

In reality, you get around 3cfm per hp for this type of compressor (that's FAD, i.e the actual air you get out of it)

I thought this, but I can understand why if I go on the devilbiss website and look up exstally how much cfm my GTi uses, its almost perfect, because the gun is 12-14cfm depending on fluid tip / air cap

and that pump produces just enough air to hold a constant spraying presure, anymore (air fed mask) I get a drop in presure and the pump cant keep up.

Surly that means the pump is producing 12-14cfm if it can constantly provide the correct presure/flow while its running

 

[esc]

I've changed my mind with what I intend to do now as there was alot of flaws you guys have put me on to (thanks for that because Ied of wasted what money I have failing)

Now I've decided to rebuild my single phase compressor get the motor going again (I hope its the cap thats blown and not the motor)

Use that one mobile powerd by an inverter (motor is 2.2kw so its doable) then I'm going to rebuild my 3 phase compressor pump, and put the pump and motor on a trolly, so I can (when I'm in my workshop and need more air) conect the 3 phase pump and motor up to the single phase compressor (if this makes sense)

So on the single phase compressor theyll be another check valve and unloading tube already plumbed in, with a quick release conector on the check valve, and I'll put a quick release conector on the 3 phase rig pump so I can just conect it up.

There will only be one presure switch, so the 3 phase rig will run all the time and I'll just use the 3phase breaker and switch thats there to turn it on and off when I'm done with it, and the unloading tube should vent the extra presure.

So I'll need a couple fittings to make this happen... However first things first....

I really need to find some replacment valves and gaskets for this compressor pump ive taken apart, where should I start?

The valves look just like this
http://www.google.co.uk/imgres?um=1...144&start=0&ndsp=23&ved=1t:429,r:22,s:0,i:154

but its not that shape size, I also need piston rings...

The compressor pump in question is an ABAC compressor...
http://www.jbltools.co.uk/ekmps/sho...ac-b3914-150t-150ltr-air-compressor-556-p.jpg

Exstally that, but single phase not 3

any ideas on where to start looking would be really appreciated!

I'll just have to hope once this pumps been rebuilt the single phase compressor will do what I want it to on the move.