Impeller clearance setting and Pump Set up

[siddiq191]

Hi,

Our plant uses vertical turbine pump for water intake.The pump capacity is 19000cum/hr and the head is 16m.It has adjusting spacer in between the rigid coupling and by adjusting the spacer thickness,impeller clearance is maintained.I want to know how they adjust the spacer according to the clearance requirement and what is the normal impeller clearance.Please explain with a case study or example.

Please explain the term FLOAT because they adjust float while setting the impeller.

Can Any Pump Maintenance professional help me?

 

[Artisi]

Would help if you identified the pump manufacturer / model etc. -also where is the operating manual that would have been supplied with the pump.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[JJPellin]

Given the information you provided, the lift setting is probably between 0.030 inch and 0.75 inch. The term "float" probably refers to the the total range of lift from touching on the bottom to touching on the top of the impeller.

Impeller lift setting depends on impeller design, wear ring design, shaft length, impeller weight, fluid properties, process temperature and more.

Johnny Pellin

 

[Artisi]

Correct, when all else fails read the instructions.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[1gibson]

Those conditions, it is an axial flow pump. Typical lift is pump bowl nominal diameter (inches) in thousandths of an inch. 60" pump, 0.060" lift. There are many considerations that go into the lift that is specified, so you need to follow the OEM instructions. If they didn't provide a value, ask. You will damage the pump if lift is too small, lose efficiency if it is too big.

The lift value provided should be specified "from free rotation." There can be some slop in the shaft couplings and/or impeller mounting hardware, so if you set the lift relative to the uncoupled pump rotor, you will lose the slop and could be a few thousandths shy on actual lift vs. what you think it is. One piece shaft on a small pump, it's going to be approximately zero. Multiple shafts with sleeve type couplings, big pump, it can be a few thousandths or more.

Anyway, to set the lift, first you will spin the adjusting plate to the point that bolting the coupling together barely allows free rotation by hand. Then remove the bolts and let the rotor rest in bottom position. Do not allow the adjusting plate to rotate. The pump half coupling may drop on the shaft, depends on how it is fitted. Don't let it smash your packing or mechanical seal! You will need a shim pack with thickness equal to the desired lift. The shim pack will go above the adjusting plate; in between AP and spacer (4 pc) or AP and motor half coupling (3 pc.) Slowly spin the adjusting plate down on the shaft, bolting the coupling together at appropriate intervals* of adjusting plate rotation, until you barely achieve free rotation with the shim pack installed. Remove the shim pack, and bolt it up, you're done.

Note that you can skip the first step (adjust to free rotation with no shim pack) but it helps to have a good idea where you need the adjusting plate, before you start messing with shim pack. You can have inches of adjustment, so starting blind wastes a lot of time.

* Interval will depend on shaft threads, it helps to have an idea how many turns you need to get the lift you want. To get the lift as close as possible, during the final check, you want the difference between the rotor dragging or spinning freely, to come down to the smallest incremental rotation of the adjusting plate. 4 bolt holes, 90*, 8 bolt holes, 45*. I say bolt holes instead of bolts, because it is not unusual for the adjusting plate to have 2x the number of holes as there are coupling bolts, to allow more precise lift settings.

It should go without saying, but all of the rotation checks are by hand or with a strap wrench for larger pumps. Or, realistically, using a box wrench on a single coupling bolt to rotate the entire rotor. Watch for any dragging as the rotation stops. You'll also be able to feel it with a hand on the shaft.