We are getting short life (2yrs.) out of the Balance drum/disc. design of a DeLaval Barrel pump. I understand the pump is no longer made but would like info on an upgrade for this design. The latest ugrade was hardened 400 series stainless. The gap starts at .005 thds.(per IOM) and opens up heating up the thrust bearing. Start temp. is 140 and alarm is at 180 with shut down at 180 F. We get 8yrs. out of IDP.
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DeLaval Barrel Boiler Feed pump 1
- Thread starter jpink
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Have had quite a lot of experience with balance drum and piston designs malfunctioning on multistage pumps. Firstly, does this pump have a single drum designed to take up 95% of the thrust with a tilting pad or heavy duty ball bearing to accept the remaining 5% of does the pump have a combined drum and balance disk or just a disk that allows the rotating element to float and find its own running position? I ask this question as there are several balance devices and combinations about.
If you only have a disk fitted that operates like a variable orifice it will run at about 0.005 thou from the stationary plate. The thrust is taken up hydraulically. On some designs, especially if pumping petroleum products, a thrust bearing was fitted to prevent the impellers running up and seizing on the pump chambers in the event of a balance disk failure. The bearing will run very hot warning the operations to shut the unit down but at least it will prevent a catastrophic failure.
Perhaps you can explain the device you have fitted in more detail and I will try and assist you better. A sectional arrangement drawing would be better still.
If you only have a disk fitted that operates like a variable orifice it will run at about 0.005 thou from the stationary plate. The thrust is taken up hydraulically. On some designs, especially if pumping petroleum products, a thrust bearing was fitted to prevent the impellers running up and seizing on the pump chambers in the event of a balance disk failure. The bearing will run very hot warning the operations to shut the unit down but at least it will prevent a catastrophic failure.
Perhaps you can explain the device you have fitted in more detail and I will try and assist you better. A sectional arrangement drawing would be better still.
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This is a balance drum/disc design with tilting pad thrust and babbit radial bearings. The tilting pad is also spring loaded. I'm wandering about increasing the hardness of the drum/disc faces and closing up the tolerance to lessen the load on the thrust bearing? It is my understanding the tilting pad thrust is active on start up and shut down and is to be idle when the hydraulic pressure takes over at full speed between drum/disc faces. The more circulation (.005 thds. clearance) the more load on the thrust bearing and thus the higher temperature? I feel as the clearance opens up from wear the more load on the thrust bearing?
I think I now have a handle on your problem.You say you have a combined drum disk design. Very popular with some US pump OEMs. This means the drum will be sized to take up most of the thrust from the impellers moving towards the driver. The drum outer dia, I presume will be about 95% of the impeller eye diameter? The disk acts as a variable orifice keeping the rotating element in equilibrium enabling the pump to operate without an ACTIVE thrust bearing.I believe the tilting pads (one set fitted inboard is that correct)??which are spring loaded are designed to ensure that the balance disk is kept away from the stationary balance valve face on pump run down when the machine slows to around 20% of full speed and the hydraulic forces produced at this speed are insufficient to keep rotating element equilibrium. We call this a pull off device and is ofter fitted to troublesome pumps. As a consequence without this device the faces will rub together and become damaged in time. I believe you need to establish the actual operating gap between the balance valve faces first of all then set up the thrust assembly to ensure that the thrust bearing can operate without heating up. I suggest you stop the pump at normal operating temperature. Attach a dial indicator stylus to the NDE of the pump shaft.Apply a few drops of oil and re-start the pump up to normal speed. After a minute or so when full forward flow is established take a note of the dial indicator reading. Depending on your set up you may wish to have someone hold off the stylus by hand until you wish to take the reading. This will save wear on the stylus tip. The difficult bit is now knowing at what tension to set the springs to. As I do not know the type of springs and compressive strength it will be difficult to complete the last piece of the puzzle.
I suggest you advise me if the foregoing makes sense so far and then we will go for the final solution.
I suggest you advise me if the foregoing makes sense so far and then we will go for the final solution.
As an ammendment to my earlier message, I should have said I would also expect an outboard set of non springloaded thrust pads installed to restrict the shaft end float away from the drive end. The thrust collar keyed onto the shaft would be double sided. Total shaft float set at 0.025"/0.030"
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