PROPER INSTALLATION OF A PIECE OF ROTATING EQUIPMENT ADDS AS MUCH TO THE LIFE OF THE EQUIPMENT AS PROPER SELECTION. Installation involves several aspects, including piping configuration, NPSHa, pipe strain, baseplates, foundations, and alignment.
When designing the piping system for pumps, some basic rules of thumb can be used to help extend the life of the equipment. These basic rules evolve around a couple of concepts:
- The pump does not create pressure. It overcomes resistance.
- Resistance is caused by the resistance to flow of a liquid in a piping system and existing pressures and elevations in the system.
- The pump is a device that adds energy to the medium being pumped.
- Flow is created by a difference in pressure.
- A pump creates a low pressure at its inlet to allow liquid in the suction piping to flow into the pump.
Rules of "Thumb" and General Discussions to Help in the Design and Sizing of Piping Systems
The suction piping is necessary to provide a means of getting the liquid to be pumped from its source to the pump inlet or suction nozzle of the pump.
KEEP IN MIND THAT MOST HYDRAULIC PUMP PROBLEMS ARE CREATED ON THE SUCTION SIDE OF THE PUMP. The following topics are general rules of thumb to consider when developing the suction piping system.
- Suction piping should be one or more pipe sizes larger than the pump inlet connection. Metering pumps with a pulsing flow require special attention. A pump with a pulsing flow may require suction piping sized for three or more times the average flow rate because of acceleration and velocity characteristics.
- Keep the suction piping as short as possible.
- Keep the suction piping as straight as possible.
- Keep a minimum of 5 to 10 pipe diameters of straight run in the piping prior to the pump inlet.
- Avoid high points in the suction piping. Go around objects instead of over them.
- Where possible, allow the piping to slope upwards toward the pump suction to reduce air pockets.
- Reducers used in the suction piping should be eccentric with the flat side of the top.
- Strainers should be used to prevent foreign objects from entering the pump. The strainer should be sized based on minimum pressure drop and not on line size.
- Valves in the suction line should be sized for minimum pressure drop, and never used as throttling valves.
- Always provide a gauge connection between the suction valve and the pump connection. The gauge connection should be located as near to the pump suction connection as possible.
- Insure that the suction piping connection to the source reservoir is sufficiently submerged or baffled to prevent vortices or drawing in air.
- Don't be mistaken in believing that a flooded suction will always provide sufficient NPSHa. Calculate the losses in the suction line to insure you have sufficient NPSH available.
- Support the piping independently of the pump. (A pump is a very expensive pipe support.)
- Use expansion loops or flexible connectors in systems where thermal expansion of the piping will occur.