Pump & Motor Speed Help Needed

[Turbo]

Bought this Ingersoll Rand compressor locally last week from an auction.

I got it fairly cheap as it wouldn't start up unless the tank was empty. I knew what the problem was - the wrong motor was fitted. It was a 2.2kw but it was a psc 2750rpm motor & hadn't the torque to start under load. It was also very badly fitted.

Why didn't they use the existing motor mounting slots & adjust the pulley position on the shaft to suit?

First thing I checked was the mains cable - found this as a fuse.

Yes, that's a very rusty hex screwdriver bit, making very poor contact with the broken fuse holder in the plug. The whole lead was replaced with some 2.5mm & a 16A plug plus I fixed some damaged wiring in the pressure switch.

But even with the wiring repairs it still wouldn't start. To check the pump was working I increased the capacitor size from the standard 45uf to 60uf. I have now got it working though only temporarily, a large step up in capacitor size is not good for the motor windings.

My decision now is to fit another 2750 rpm motor with capacitor start/capacitor run for better starting torque or fit a 1400 rpm 4 pole motor which should be better again though more expensive?

The good news is that the pump is working well & it is able to keep up with the die grinder. It fills up the 200l tank in 5 mins from empty. The bad news is that it's not the original IR pump, it looks like one of the generic pumps sold by machine mart, clarke & ebay.

Now to the main reasons for my post. This is an appeal to anyone who has a belt drive 3hp compressor, especially clarke ones that have the same pump. I would like to know what speed your motor is & what the approximate pulley sizes are.

This is so I can work out what speed the pump should run at. I have contacted the sellers on ebay & I'm getting anything from 1200 to 2800 rpm for pump speed! At the minute it is running at 930rpm & according to IR a cast iron pump should run at 1000rpm, but it's not an IR pump!

I am still undecided on a 1400 or 2800rpm motor, so it would be interesting to know what's commonly used. I can adjust the pulley sizes to suit either speed.

Thanks for your help.

 

[Ton-up]

We have a three phase IR comp like that at work. I can have a look tomorrow what size the motor/pump is but I doubt it is 2750 rpm.

 

[mike 109444]

I wonder if you have a "triggers broom" there Where some one has taken BOTH the pump and motor from a smaller clarke machine and put it on the bigger tank ?
If you can match the pump to one of the clarke range of compressors or there spares pumps then they usually quote there machines as something like "super quiet running nnn speed motor". Are there any marks on the paint around the pump mount plate to show where a larger pump might have been mounted.
Wonder what amp rating a 1/4 drive bit is . think some one did post a pic of various items verses rating used in plugs ie tin foil, nail ect.
Good luck with the project.

 

[rtbcomp]

If it fills the tank in 5 mins you can't be far out with your pulleys. As long as the unloader's working correctly I'd be inclined to fit a 3hp motor of the same speed as the existing one.

 

[dannyp]

on my clarke the motors are 2750,

what ive found to be best trick cobbeling compressors up over recent years is to put intentionaly the wrong size pully on the motor, if you don't know what it needs put to small a pully on then measure the current drawn when it's running just before it cuts out from that you can guestimate the power the motor is needing to provide to the pump to run at that speed, if you have a 4kw motor and it's only pulling say 2 kw go for the commonly avalible pully that spins it upto twice as fast

 

[rtbcomp]

Be wary that driving a pump too fast can cause a reduction in output. The piston is on its way back down the bore before all of the air has transferred to the tank.

 

[normspanners]

If it runs up to pressure ok now, and is not overloading as danny says check with a clamp on, why not fit a timed unloader solenoid to reduce the starting pumping loads, cheaper than a motor and always a welcome addition to any compressor andif the motor does cause problems later the unloader will aid in cold weather anyway.

 

[Turbo]

Thanks for your replies.

We have a three phase IR comp like that at work. I can have a look tomorrow what size the motor/pump is but I doubt it is 2750 rpm.

That would be great.

If you can match the pump to one of the clarke range of compressors or there spares pumps then they usually quote there machines as something like "super quiet running nnn speed motor".

Whats looks like an identical pump is listed on their website & all it says is 14cfm output, 2.2kw motor needed but no mention of what speed it should run at. I've sent them an e-mail, hopefully I'll get a more accurate reply than the ebay traders.

If it runs up to pressure ok now, and is not overloading as danny says check with a clamp on, why not fit a timed unloader solenoid to reduce the starting pumping loads, cheaper than a motor and always a welcome addition to any compressor andif the motor does cause problems later the unloader will aid in cold weather anyway.

I like the sound of this idea, anything to save money is good news to me (must be the Scottish blood in me) .

Unfortunately any purpose made timed unloader solenoids start from £50, do you know of anything cheaper?

I could always make something up using these items from ebay.
http://www.ebay.co.uk/itm/151034-El...hash=item41b29656df:m:mCqQfVxY-Vq74auI0nDnqmA
http://www.ebay.co.uk/itm/AC220V-23...hash=item3ae397240a:m:mXiVb6Y9Q0u3mnZyjLnPhCA

I might have a fuel solenoid somewhere that would be suitable, not sure about the timer - I'll have a look tomorrow.

 

[rtbcomp]

...

I like the sound of this idea, anything to save money is good news to me (must be the Scottish blood in me) .

Unfortunately any purpose made timed unloader solenoids start from £50, do you know of anything cheaper?

...

I've used washing machine solenoids with compressed air. They're fine if there's no oil in the air. If you power them on continuously wire a small bulb (eg microwave oven lamp) in series to stop them overheating.

 

[Bill Edwards]

Easiest and cheapest method to prevent it struggling to start when the tank is full is to extend the pipe between the compressor and check valve - essentially making it like a small tank. It'll get up to full speed before it's working against pressure.

 

[normspanners]

I have already done that with my portable machine I extended the pipe and used soft copper that now goes all the way to the rear of the motor and has a coil at the fan housing so that the air is drawn over it. Then a loop/ length of hydraulic hose to further extend it, But it can still struggle at times especially in cold weather, because any closed pipe will still start to raise the pressure even the pressure to overcome the check valve , whereas if open to atmosphere as soon as it leaves the manifold it cannot build any pressure, apart from the pressure it creates to open the outlet valve, which although small does cause some resistance. even 5 psi can be unsurmountable when added to the motor rotor ,flywheel thick oil stiff belts etc etc all happening together.
I have just gone through the same scenario with a large compressor that was blowing a 20A c rated mcb because it had a pressure fed solenoid valve that unloaded the inlet valves the machine would start, fine full of air, but first thing in morning it tried with no air in the tank and therefore no unloading and pop it would trip!