Running 2 compressors v. 1

[ZooCity]

Considering running two 7.5 hp screw compressors v. buying a new 15hp.   The main benefit of running 2 is obvious- redundancy... better to have one press running than none right?  In our location there is nowhere I can rent a big enough electric compressor if ours goes down so it's a major consideration.

How bad would the loss of efficiency be v. a single 15hp unit?  Anyone running their air this way?

Both would be total air systems with chillers and tanks, so my guess is that these would run from their respective tanks into a joint tank and then down stream to the air loop?

[Gilligan]

Of course you would lose efficiency (Brian can better answer that more exactly), BUT, there is nothing efficient about being dead in the water if your 15HP goes down!

[Binkspot]

IMO like I said in another thread a perfect set up would be two compressors, dryers and tanks that in the case of a failure one could be isolated and the other used. You have the added benefit of more volume with the two tanks. Set them up so one is a high and the other low. The primary would kick on lets say 120psi the second at 110psi. Go a little further and add a rotary switch tied into the pressure switches where you could run one as the high for a few months then switch to the other. Run a large cross over between the two tanks with a valve to connect the two. Unless you are running like a raped ape the second one should hardly run. I would also consider coming off one of the tanks with a 3/4" line, ball valve and Chicago fitting, if you were ever to go down rent a larger gas or diesel compressor and just connect it to the Chicago fitting. Also consider you already own the one and adding a second would be a cost savings.

[Doug B]

  We have 2 in line. Turn of a valve and a flip of a switch and we never have to worry about
one going out. Always have the backup.

[ebscreen]

Our rotary uses two piston type compressors as the storage tanks. If the rotary goes down all we have to do
is turn the pistons on. Redundancy is incredibly important in this industry. And like Brian said, if you do go down just get
a big old diesel compressor and stick it outside. Some shops have generators outside just in case...

[tonypep]

We run 2- 50H screws in tandem. One can almost keep us going but they work in tandem so they don't get overworked. Pretty smart system.

[Sbrem]

We also run 2 up, alternating...

Steve

[Admiral]

I bought a nice used 15hp screw for $4400, we use that and have the old 7.5 recip connected with the valve off and if we have a problem we will turn the valve of the new compressor, start up the old one, and open the valve when it's pressured up.  Total downtime would be 30 seconds tops.

I would consider doing that instead of just 2 7.5s.  Either way would work though, it really just comes down to costs, if the operating cost of both vs one is 500 more a year I would definitely go for the 15hp screw and run just that one and have the old one setup for backup..

[ZooCity]

Ok, I'm concluding that two is ideal but they can't both be running full tilt.  As suggested by you all, one can be primary with the second kicking in as needed all feeding another tank.  And switching the primary is a golden idea too in order to keep wear even.

If we have two 7.5s running non stop then I would wager that yes, we'd be better off with a single 15 or 20 and storing the 7.5 as an emergency backup or running it tandem with the 15 or 20.  With two going full bore than I would guess that electrical costs would offset benefits in a few years.

I think I'm just going to look for the largest I can find to run in tandem with the 7.5  One will have to be out on the floor though as our compressor room would only have space for two vertically oriented, not two horizontals and our current is horizontal. 

Love this forum.  Thanks to all for the replies and thanks Dave for the PM.

[Binkspot]

Buy the compressors as split units, put the compressors in the compressor room and mount the tanks to the celing up out of the way. As long as you can drain them you would be fine. You could even stack the compressors.

[Gilligan]

Buy the compressors as split units, put the compressors in the compressor room and mount the tanks to the celing up out of the way. As long as you can drain them you would be fine. You could even stack the compressors.

This would allow for a larger/more creative after cooler as well leading to the tanks... or is this just over kill?

[TCT]

We have 2 compressors our original 7.5HP(10 slowed down) and a 20HP neither of which are screw type. Also 2 chillers, one handles up to 24CFM(I think) and the other is somewhere in the 60CFM. Add to that 500gal+ of tank. The whole thing is waaaaaay more than I need but I got a absolutely stupid crazy deal on the big chiller, compressor and a 240 gal tank. Ours is set up so any 1 item can be isolated and still leave the rest running. The 7.5 could not run everything on it's own, but in a emergency the 7.5 could run like a mother and fill all that tank space and not be ran all the time. Not ideal, but it could happen. I also have the luxury of Grainger less than 5min away(sorry Chris  ) Our compressors are also in the basement so them not being a quieter screw type really is a non issue for us.

The extra tank space is a cheap way to add some capability in a emergency situation...

[beanie357]

Cheap ingersols at tractor supply.
Chillers at graingers.
Parallel systems.
Cheap, noisy, redundant.
Never more than one press down if problem.
2 cheapie homey types for backup, which cover any one press.
Damm I am cheap.

[bimmridder]

I ran a pipe when we set up the new shop (something like Simpleair?) I used a large diameter pipe until I got to the drops to equipment. The larger diameter acts as a tank also. I don't know air consumption theory, but imagine how much more air a 3'' ID pipe will hold versus a 3/4'' pipe. The stuff costs more, but SO easy to run. Add drops when and where you want. And take it with you if you move. Just a few peripheral thoughts

[jvanick]

If my google-foo was correct and the geometry checks out, each foot of 3" pipe holds roughly 1 gallon.  So yes, that is one hell of an 'extra' air storage tank.