External Oil pump for a Mycom W8B using a VFD

[jeffp1956]

Greetings Fellow Engineers
I have a 150 HP Mycom W8B running in a mid temp fruit warehouse. Due to efficency gains from retrofiting my evaporator fans with VFD's My load has decreased to the point that this machine is running 25 to 50 % load most of the time and I am not liking the high compressor disch temps this condition generates. My solution is to install a VFD on this compressor. Because I dont have the floor space or electrical capacity to install an addiional smaller compressor. I have aquired an AB VFD and a FES / GEA Gforce prosessor panel configured for a recip with a VFD and am in the process of having them installed. My quandry is that I am unsure how to intergrate the required oil pump in to this. The oil pump suction is going to come from a modified oil strainer cover as for the oil pump disch as far as I can tell there are two stock oil output pump ports on the W8B. One that goes to the unloader pistons and one that goes to the oil filter, oil cooler and then to the bearings. I am unsure of how to pipe these. If any of you guys have done ths I would appriciate some direction Mycom USA is no help my Ref contractor has never done one of these modifications either so any help you guys can offer is appriciated

[RANGER1]

Jeff,
It appear that you want to install a remote pump on this compressor?
I would first ask why, as what minimum & maximum speeds you want to run this compressor.

Mycom have a low speed oil pump option which you can install, this is suited for speeds below 800 rpm ( would have to confirm that).
Also 8WB have I think min speed650 rpm max speed 1200rpm

The discharge temp can run up to 130-140 degC max no problem.

- If you install a remote pump (which I can't see as necassary) you can turn oil pump suction strainer say
1/4 or 1/2 turn then remove 3/4 plug to install fitting. This will block of oil to suction gallery of pump.
- REMOVE OIL PUMP DRIVE then put pump back in.
- discharge of pump would have to include a filter suitable before feeding oil to oil cooler & unloaders.
Existing cuno filter & housing would be redundant, as all ports are cast into compressor housing

Note the existing unloader fitting has orifice in it so to much oil does'nt go to unload piston, try to re-use it or you will have trouble.

[jeffp1956]

Jeff,
It appear that you want to install a remote pump on this compressor?Yes I do
I would first ask why,for proper oiling at lower RPM's as what minimum & maximum speeds you want to run this compressor.Maxium is current full motor rpm 1200 RPM minium is as low as I can go

Mycom have a low speed oil pump option which you can install, this is suited for speeds below 800 rpm ( would have to confirm that).I was told it would not work at 1200 rpm
Also 8WB have I think min speed650 rpm max speed 1200rpm my contractor told me mycom said 850 minium RPM

The discharge temp can run up to 130-140 degC max no problem.my overheating problem has been the water jacket temp gets to hot

- If you install a remote pump (which I can't see as necassary) you can turn oil pump suction strainer say
1/4 or 1/2 turn then remove 3/4 plug to install fitting. This will block of oil to suction gallery of pump.
- REMOVE OIL PUMP DRIVE then put pump back in.
- discharge of pump would have to include a filter suitable before feeding oil to oil cooler & unloaders.
Existing cuno filter & housing would be redundant, as all ports are cast into compressor housingI understand that I am just worried about proper lubrication of crank bearings

Note the existing unloader fitting has orifice in it so to much oil does'nt go to unload piston, try to re-use it or you will have trouble.

thank you for your repily

[RANGER1]

Jeff,
850 rpm is for standard oil pump, so if you install low speed pump I think it can go down to 650rpm.
Mycom have a minimum speed of compressor of 650rpm, so not recommended you go below that.

We have a plants that run at constant 700 rpm with low speed high volume oil pump.

[jeffp1956]

what about running the LSHV pump at 1200 RPM ?

[RANGER1]

Good question I don't know, but would you ever run it at that speed?
We would normally never go over 1000rpm which would be OK.

You could instal another relief valve set at say 60 psi (adjustable) to relieve any excess oil pressure directly back into sump above oil level.

You should also get water jackets & cooling water rectified no matter what.

[RANGER1]

jeff,

standard oil pump 22 litres/min

low speed pump 29.2 litres/min

you need to select a pump based on above, then speed of machine would mot matter.

[Segei]

May be it is better to clean water jacket. If you have low load, you can increase suction pressure and this will help to reduce discharge temperature.

[jeffp1956]

Ranger
Water Jackets have been recently cleaned and oil cooler was replaced at that time I have good water flow to the water jackets and good return flow to the water tank. At this time of the year (almost out of stored product ) and in winter the compressor can run at 25% capacity most of the time this also happens during the winter too. This causes high discharge temps mostly with an occasional high water jacket over temp, but probably only 1 or 2 trips a year. it never trips out on high discharge temp but it gets very high and I dont want to slow cook this compressor over time and that was the whole reason for the vfd. My concearn now is what problems will be created by running a low rpm oil pump at 1200 RPM, I need to run this machine at that speed to satisify higher load requirement encountered during the day with out turning on the next machine in the engine room control scheme which is a mycom 200 hp screw. You mentioned a high psi bypass regulator dumped back to the compressor sump. Is high preassure a result of running the low RPM pump at high rpm ?

[jeffp1956]

I have also come to the conclusion that using an external oil pump on this compressor is impratical.

[RANGER1]

Ranger
Water Jackets have been recently cleaned and oil cooler was replaced at that time I have good water flow to the water jackets and good return flow to the water tank. At this time of the year (almost out of stored product ) and in winter the compressor can run at 25% capacity most of the time this also happens during the winter too. This causes high discharge temps mostly with an occasional high water jacket over temp, but probably only 1 or 2 trips a year. it never trips out on high discharge temp but it gets very high and I dont want to slow cook this compressor over time and that was the whole reason for the vfd. My concearn now is what problems will be created by running a low rpm oil pump at 1200 RPM, I need to run this machine at that speed to satisify higher load requirement encountered during the day with out turning on the next machine in the engine room control scheme which is a mycom 200 hp screw. You mentioned a high psi bypass regulator dumped back to the compressor sump. Is high preassure a result of running the low RPM pump at high rpm ?

Yes relief valve back to sump for excess oil pressure.
I don't have information on maximum speed for low speed oil pump, but would hazard a guess it would be 1000rpm.
I wouls install a relief valve at outlet of pump & adjust if needed. Mycom regulate oil pressure at end of oil circuit so if a relief was installed it would be set higher due to pressure drop in oil circuit.

I have installed a remote pump, but not on a Mycom, all went ok.

[Segei]

Ranger
Water Jackets have been recently cleaned and oil cooler was replaced at that time I have good water flow to the water jackets and good return flow to the water tank. At this time of the year (almost out of stored product ) and in winter the compressor can run at 25% capacity most of the time this also happens during the winter too. This causes high discharge temps mostly with an occasional high water jacket over temp, but probably only 1 or 2 trips a year. it never trips out on high discharge temp but it gets very high and I dont want to slow cook this compressor over time and that was the whole reason for the vfd. My concearn now is what problems will be created by running a low rpm oil pump at 1200 RPM, I need to run this machine at that speed to satisify higher load requirement encountered during the day with out turning on the next machine in the engine room control scheme which is a mycom 200 hp screw. You mentioned a high psi bypass regulator dumped back to the compressor sump. Is high preassure a result of running the low RPM pump at high rpm ?
Why do you think that your discharge temp. will be lower with VFD? I assume that refrigerant is ammonia. What are suction and discharge pressures?

[IceMan_4000]

Why do you think that your discharge temp. will be lower with VFD? I assume that refrigerant is ammonia. What are suction and discharge pressures?


With a VFD he will no longer need to unload the machine for low capacity control. The unloaded condition is what is causing the increase in discharge temperature. The lower amount of cool suction gas entering the cylinder makes for higher discharge.

[RANGER1]

It also needs about 50 litres/min of water going through heads etc for good cooling.
If has small shell/tube oil cooler it may need tubes cleaned.
Usually 2 feeds of water in, 1 through oil cooler & 1 through discharge cooling jacket.

[Segei]

With a VFD he will no longer need to unload the machine for low capacity control. The unloaded condition is what is causing the increase in discharge temperature. The lower amount of cool suction gas entering the cylinder makes for higher discharge.
Compressor has 25% load. You mean that VFD can reduce speed by 4 times and compressor will be loaded at 100%. Most likely it will be 50% capacity even with VFD. Will it help to discharge temperature? May be better reduce suction super heat or better control suction and discharge pressures.

[RANGER1]

I think jeff mentioned 25 to 50% loaded at 1200rpm.
If he drops down to 650rpm it might be 75 to 100%.

Of course if jeff tells us suction, discharge pressures & discharge temps etc it would help considerably.

[IceMan_4000]

maximum speed for a mycom low speed oil pump is 800. So if you wanted to go to low speed you would be restricted to 650-800