Centrifugal vs Gear Pump for lube system
Centrifugal vs Gear Pump for lube system
(OP)
We are design a lube system for compressor bearings for 60 gpm and 100 psig. In order to scavenge oil and air, our reservoir will operate at 5 psia pressure, partial vacuum. Vendor says a gear pump needs 16' NPSH, we have 13' NPSHa. Vendor has a centrifugal pump that only needs 3' NPSH, and we're considering using the centrifugal. I've not seen any lube systems with centrifugal pumps, only gear pumps. What are the disadvantages of using centrifugal pumps in a lube system?
Larry





RE: Centrifugal vs Gear Pump for lube system
I would not be very much inclined to use a centrifugal pump for such an application, and I'm presuming that the proposed gear pump is of the common two meshing external spur gear configuration.
Instead, I suggest that you consider a "Gearotor" pump configuration. This is an internal-external gear pump type that has some very nice characteristics. The void cavities open and close with relatively gentle rates of change in the void volume. (Flow into and out of the void spaces is parallel to the gear shaft axis.) As a result, the NPSHr is much smaller, and the operating noise level is usually much lower.
I've used the "Gearotor" style pumps very successfully, and where appropriate, I consider them to be a preferred type even though they may seem a bit more expensive initially. The pumped fluid serves as the pump lubricant, so your compressor lube oil system should be an excellent application.
RE: Centrifugal vs Gear Pump for lube system
Efficiency in the smaller sizes like yours.
Difficulty at startup when the oil may be below normal temperature and much more viscous. You could eliminate the suction strainer with a centrifugal, but there could still be difficulties
For scavenge duty, the presence of air is almost inevitable. This can stop a centrifugal from pumping; a decent gear pump will handle it OK.
I prefer screw pumps, but for your light duty, a gear pump, as the vendor and ccfowler suggest appears the best solution.
3 out of 3 recommend gear pumps.
Cheers
Steve
RE: Centrifugal vs Gear Pump for lube system
Larry
RE: Centrifugal vs Gear Pump for lube system
OldSohioEngr tells us the vendor said, I quote, "a gear pump needs 16' NPSH". This is a generalization difficult to accept in view of the fact that the majority of rotary pumps operate with suction lifts.
One is inclined to ask whether there is a way of improving the NPSHa by 3' (23%) so the proposed gear pump becomes acceptable. Otherwise it is probable another vendor could offer a gear pump suitable for the available NPSH.
RE: Centrifugal vs Gear Pump for lube system
Larry
RE: Centrifugal vs Gear Pump for lube system
RE: Centrifugal vs Gear Pump for lube system
Larry
RE: Centrifugal vs Gear Pump for lube system
Majore spec data:
1. Flow rate: 5l/min @ 40psi
2. Brushless moter
3. Variable speed moter controller
4. 24vdc operating voltage
5. Operating life: >30,000hrs
6. Fluid type: water
Thank you.
RE: Centrifugal vs Gear Pump for lube system
RE: Centrifugal vs Gear Pump for lube system
regarding the use, in general, of centrifugal vs. rotary pumps in lube oil service:
I am familiar with the GE industrial type gas turbines and they evolved in the following way:
1. frame 5/6/7/9 std design (i.e. not F class)
1.a main lube oil pump: mechanical (pd) type driven by the auxiliary gearbox (i.e. driven by the gas turbine)
1.b auxiliary lube oil pump (100% capacity): submerged centrifugal type pump with AC motor
2. frame 6/7/9 F class units
2.a lube oil pump: redundant submerged centrifugal type pump with AC motor in separate (off base skid)
3. all frame sizes
emergency lube oil pump: submerged centrifugal pump with DC motor
so... as you can see there are as many designs as opinions...
saludos.
a.
saludos.
a.