I want to install a VSD on a Sullair B32 screw compressor controlled via M&M micro.

[Lodiev]

My newest project on energy saving is to control a Sullair B32 screw compressor with a VSD according to demand.
The only problem i can for-see is two things,1) What will the Liquid injection do at low speed? 2) Will the lube oil at low speed be adequate for the lubrication of the bearings and rotors?
What are the minimum speed on a screw compressor with a fixed slide?

[RANGER1]

In general liquid injection for oil cooling will be less as long as whatever you are using can control it & react quick enough if sudden load changes.

I can't be specific for Sullair as I don't know

Most screw compressors generally can run at min speed of 1440rpm

If oil pump is driven off compressor you will have problems as pump may not keep up on min speeds .
If compressor driven pump you may have to consider remote oil pump & suitable controls.

[Lodiev]

In general liquid injection for oil cooling will be less as long as whatever you are using can control it & react quick enough if sudden load changes.

If oil pump is driven off compressor you will have problems as pump may not keep up on min speeds .
If compressor driven pump you may have to consider remote oil pump & suitable controls.

So u think the liquid injection would not be a problem as long as the valve controlling it can keep up with a sudden temp change at the discharge gas? No liquid flooding in the oil separator?

I forgot to say that this is a booster compressor running a suction of -45 and a discharge of -12 with Ammonia.

Do u suggest then that i stop and start the remote pump at a certain speed, and at what speed do u think i should do this?

[RANGER1]

Lodiev,
Booster duty oil cooling load is resonably small , but as long a valve has enough turdown it should control .
What type of valve do you have for liquid injection?

If machine already has remote oil pump just leave as is & run it all the time , or how is it controlled at the moment?

[Lodiev]

The package does have a pre-lube pump at present, i have done the maths and its seems to be big enough to cope with the demand of the screw at full Rpm.
At present i have a Parker Y830 expansion valve with a 30 ton orifice in controlling the liquid injection to cool the discharge gas and oil.
Its a existing package witch i have rebuild-ed and are going to install at one of our plants, so that leaves me with the option to do what i want with the controls.

[Segei]

The package does have a pre-lube pump at present, i have done the maths and its seems to be big enough to cope with the demand of the screw at full Rpm.
At present i have a Parker Y830 expansion valve with a 30 ton orifice in controlling the liquid injection to cool the discharge gas and oil.
Its a existing package witch i have rebuild-ed and are going to install at one of our plants, so that leaves me with the option to do what i want with the controls.

TEV run fine at capacities above 50%. However, at capacities 30-40% or lower it can start "hunting" and can overfeed.

[Lodiev]

TEV run fine at capacities above 50%. However, at capacities 30-40% or lower it can start "hunting" and can overfeed.

Well as mentioned by Ranger1 the minimum speed will be at +- 1440 Rpm so if i am right this is about 45% to 50% (43.2%) seeing that full speed is 3000 Rpm, so hopefully it will work fine, but if u think this will be a problem lets discuss it and see what will work in the TEV's place.

[RANGER1]

Lodiev,
Not familiar with the Parker valve but if its same as Danfoss TEAT which bulb is mounted on dicharge line & controls discharge temp .Injection is into specific liquid injection port on machine .
Another back up is to use a thermostat .

[Lodiev]

Yes it is the same except for the Y830 TEV also use the discharge pressure to allow it to open and close very fast. It senses with the bulp and uses the equalizer port to set(set at a constant pressure) the wanted temp.

[Magoo]

Hi Lodiev.
I am not formilar with Sullair compressor, is the capacity control a slide valve?. What sort of starting system is now used for booster motor, DOL, auto trani., or star delta.
A lot of new systems here now are using VSD's and ramp to 50% then fully load compressor to 100%, then capacity control is by VSD, min speed 50%, interfacing the M&M micro could be a mission as normal stop start outputs, and capacity control on the slide. Suppose you could use that function to control VSD.

[sterl]

Not that I am suggesting you put a Frick Viper drive on that machine: but they have developed a mountain of data on the use of screws at low speed including some experience applying them to some of their older machines....With oil circuit externally cooled they running ball and roller bearing compressors at less than 20% synchronous speed. With some styles of sleeve bearing machines: The oil circuit requires some interesting re-plumbing essentially because the bearings want just about the same oil flow while the rotors want less...And the motor ventilation is a considerable factor as well. many larger motors require outside fans when the motor is slowed to less than 30 or 40% speed on a constant torque load.

[Lodiev]

Hi Lodiev.
I am not formilar with Sullair compressor, is the capacity control a slide valve?. What sort of starting system is now used for booster motor, DOL, auto trani., or star delta.
A lot of new systems here now are using VSD's and ramp to 50% then fully load compressor to 100%, then capacity control is by VSD, min speed 50%, interfacing the M&M micro could be a mission as normal stop start outputs, and capacity control on the slide. Suppose you could use that function to control VSD.

The B32 Sullair does not have a slide valve at all, but a butterfly valve in the suction port on the compressor.
They previously had statematic (liquid) starters. The motor is a 185 kw Dutchi and to get a VSD for this size was very difficult.
I already spoke to the M&M agent here and he confirmed that M&M does do this and will program the Micro to my need.
The compressor will start with the butterfly valve fully closed and ramp up to 100% then the valve will fully open and the speed will come down according to load, if 50% speed is still to much then the valve will close according to load.

[Lodiev]

Not that I am suggesting you put a Frick Viper drive on that machine:

Haven d heard of this drive can u maybe give me some detail on it?
As i just mentioned it is a 185Kw motor and it will be running a minimum speed of 50%, do u think it will overhead at this speed?
As far as the rotor oil feed goes i am not sure if it will overfeed at low speed seeing that the oil are not pumped into the rotors but sucked with pressure difference.

[phillipablack]

We offer complete retrofit services for Sullair machines. I have installed VFD's on B32's previously. You'll need to remove the screw driven oil pump and replace it with an electric pump motor assembly. M&M CCS panels can be retrofitted to provide the VFD interface for capacity control. We'd be glad to help!