Is it worth making this compressor work...

[JeremyFXDWG]

I was given a basically like new ( it has 26 hours on it) Joy Twistair Rotary Screw compressor with the built in cooler. It is a 120gal 7.5hp 3 phase with VFD control. I think it is from a year or so before Joy went out of business.

My thought was to put a 7.5hp single phase motor on it with a pressure switch and Mag starter and basically skip the VFD and 3 phase. The VFD causes the compressor to run all the time and I really just need it to cycle on and off when I need air. Is this even possible with a rotary?

I am trying to decide between doing this or just getting rid of it and buying a Quincy or Eaton 7.5hp piston compressor.

I want to be able to run a decent sized blast cabinet as well as the usual gamut of air tools. Maybe a couple die grinders or DAs at once.

Thanks,
Jeremy

 

[38Chevy454]

First do you have 3 phase where you want the compressor? Second sounds like you have a real nice compressor that if you decide not to use would be good sale value.

I am not familiar enough with rotary compressors to knwop whetether cycling on and off is a problem or not. I only have piston type. I do know that places I have worked where there was a fairly constant demand for air the rotary compressors were used.

 

[d110pickup]

No; that compressor is absolutely worthless. . . . . . . . .




Put it on a pallet and ship it to me and I'll make sure it's disposed of properly.

 

[Jim Johnstone]

I'll even pay the shipping to make sure it's disposed of properly . I'm just that kind of guy.

 

[shanker]

I'de suggest selling it as is, and getting a compressor better suited to your needs & environment.

yOu can get ALOT of compressor for the $$ that one will bring

 

[Zrexxer]

It's been my observation that screw compressors are just about impossible to sell on the secondary market by an individual. They're typically three phase, as the OP's is, and most potential buyers can't power them, and the industrial buyers who do have 3 phase power aren't purchasing used compressors off of Craigslist.

You'd be unlikely to find any affordable reciprocating compressor that could produce that kind of air delivery; I'd see if you can make it work for you.

 

[JeremyFXDWG]

Thanks for all the offers for disposal assistance...

3 phase is a no go. There is only one phase primary on my street. I would have to pay to bring the other 2 phases in for almost a mile.

I might try and sell it and wee what i can get but Like posted above i don't know what it will bring of craigslist. For 6-700 bucks I can get it running single phase off a pressure switch I think. I know from an electrical standpoint it will work i just don't know if a rotary has any limitations to working that way.

Jeremy

 

[rsanter]

the VFD and screw drive setup will save a ton of money in a buisness that needs air regularly but the demand varies

if you are going to use it like a hobby guy and just run it now and again then sell it and buy what you need

bob

 

[Professur]

Or ...... you could look up building a 3 phase rotary converter.

 

[JeremyFXDWG]

I thought about the converter but it does not solve the vfd problem of the compressor not shutting off.

 

[Grinder Bill]

Do you have access to a Owners Manual? I'm not familiar with Joy rotaries (screw or lobe?)but I have a lot of experience with AtlasCopco in plant environments. Rotaries are designed to run continuously and unload the compressor when required. To save power they can be configured to shut down after a preset time, say 5 minutes, then restart and load on demand.

 

[930dreamer]

Could you run 3 phase from a converter into the compressor vfd? More info needed.

 

[May Pop]

There are also VFDs that convert single phase to 3 phase.

 

[JeremyFXDWG]

Yes.. I can use a converter and run the compressor "as is" on 3 phase. The issue with that is that the minimum run time for the compressor is 10 min. So if it just needs to top off the tank it will run for a minimum of 10 min.

I have to separate issues. One is the 3 phase or single phase and the other is making the compressor on/off cycle instead of going to an idle for 10 min.

Jeremy

 

[930dreamer]

Yes.. I can use a converter and run the compressor "as is" on 3 phase. The issue with that is that the minimum run time for the compressor is 10 min. So if it just needs to top off the tank it will run for a minimum of 10 min.

I have to separate issues. One is the 3 phase or single phase and the other is making the compressor on/off cycle instead of going to an idle for 10 min.

Jeremy

Does the compressor include the vfd, if so what are the specs for it. Do you have any pics?

 

[justanengineer]

If the VFD takes a single phase input and you have a 220 line with enough amps to run it, you have about 5 mins of wiring to do. If the VFD is 3 in 3 out, you need a different VFD.

 

[slimpickins]

Can you post a pic? I googled the description and some of the models that come up look a lot like one of the two compressors I have in my shed.

A friend got them for free. He's keeping one and he gave me the other one. I haven't had time to look at them closely. Now I guess I should. I don't think mine are 3 phase.

Does yours have the cooling unit for drying the air? I'll snap a pic and post it later for comparison.

 

[Motown 454]

Maybe you could trade it in towards a piston compressor?

 

[Vicegrip]

Yes.. I can use a converter and run the compressor "as is" on 3 phase. The issue with that is that the minimum run time for the compressor is 10 min. So if it just needs to top off the tank it will run for a minimum of 10 min.

I have to separate issues. One is the 3 phase or single phase and the other is making the compressor on/off cycle instead of going to an idle for 10 min.

Jeremy

There is a reason for this. Screw compressors are very sensitive to oil pressure issues. Like a car motor they do not like to start stop a lot. They also are made to mesh and run well when in a design temperature range. When in unloaded condition they do not draw as much power as when compressing. They are tops for high demand use profiles but are not so good for occasional demand.

I might be inclined to clean it up real nice and sell it. It is not a good fit for a now and then use profile unless you get a real big storage tank. Rigging it to start stop a lot will likely shorten its service life.

 

[Norcal]

A VFD above 3 HP, assuming it can have phase loss protection disabled will need to be derated 50% so for a 7.5 HP motor a 15 HP VFD will be required, (3 HP & less are avail. for single phase input w/ no derating).

 

[REAL HOT SCHITT]

i was given a basically like new ( it has 26 hours on it) joy twistair rotary screw compressor with the built in cooler. It is a 120gal 7.5hp 3 phase with vfd control. I think it is from a year or so before joy went out of business.

My thought was to put a 7.5hp single phase motor on it with a pressure switch and mag starter and basically skip the vfd and 3 phase. The vfd causes the compressor to run all the time and i really just need it to cycle on and off when i need air. Is this even possible with a rotary?

I am trying to decide between doing this or just getting rid of it and buying a quincy or eaton 7.5hp piston compressor.

I want to be able to run a decent sized blast cabinet as well as the usual gamut of air tools. Maybe a couple die grinders or das at once.

Thanks,
jeremy

i have a 160 cfm atlas copco diesel, screw comp.
Atlas and sullair are legendary.

The screw comp has to be run full time when being used and has to be set up with air pressure regulator, whereas the piston will startup when on demand?.

If you want a continuous supply of air at large doses the screw type is superior and will last longer and smoother to run.
But....if you neglect service and need parts?, you will need deep pockets of cash.