Design Considerations for Equipment and Piping Layout: The Ins and Outs of Pumps
This is the second in a four-part series on equipment and piping layout. This article discusses the equipment layout considerations for pumps, as well as guidelines for the pump’s suction and discharge piping.
The first article provided guidelines for vessels, cooling towers, and compressors. Guidelines for piping and pipe rack layouts will be discussed in the third article. The series concludes with the special requirements for heat exchangers, valves, and instrumentation.
Pumps Have Many Needs
Pumps move liquids and slurries from one location or piece of equipment to another, through piping that is under pressure. The material being moved can be hot, cold, or ambient temperature. The suction and discharge lines are generally located on the side or the top of a pump.
Centrifugal pumps are most commonly used in industrial and commercial settings, although reciprocating, rotary, and diaphragm pumps may be preferred for particular situations. Most pumps are driven by electric motors. Sometimes, steam turbines drive pumps that are used for backup during power failures. Diaphragm pumps are driven by compressed air.
A primary consideration in pump layout is to place every pump close to the equipment that provides material to the suction inlet of the pump. Ideally, the suction piping is as short and straight as possible to minimize friction losses.
Another important consideration is that the location be consistent with the pump manufacturer’s specifications, as well any design and process requirements by the project owner, so that the pump provides sufficient suction and discharge pressure.
Past layout practices often located pumps under pipe racks. But in recent years, many pumps carrying flammable materials have been moved away from pipe racks to limit damage in case of a pump fire.
Mechanical engineers must also ensure that the pump location will:
- Provide easy access for pump and motor repair, replacement, and regular maintenance. For example, ensure that pump lubrication and cooling systems can be properly serviced. Also, areas around pump seals and bearings need to be accessible for service.
- Avoid potential obstructions in all directions. When everything is installed, will any pipes or valves be in the way? Make sure that the pump can be removed without removing the isolation valves.
- Comply with the owner’s specifications for pump piping, especially straight run suction line requirements. Also, other codes may apply if the pump is used in fire water service.
Piping engineers must look at numerous factors when designing the pump’s suction piping and discharge piping. The following guidelines are a sample of some industry standards and good piping layout practices.
Pump Suction Piping
Suction piping is usually one or two line sizes larger than the pump nozzle. If the suction line is two line sizes larger than the pump nozzle, use a block valve that is one size larger than the pump nozzle. Provide a drain between the block valve and the pump nozzle.
Keep suction piping as short and simple as possible to minimize friction losses and flow turbulence at the pump. The flow will be more smooth and uniform when following the API recommendation to have a straight run at least 5 pipe diameters (based on the nozzle size) between the nozzle flange and the first tee, cross, valve, or strainer. This will reduce the possibility of pump cavitation. The forces and moments on the pump nozzles created by the suction piping also need to kept below manufacturer allowables.
Some other key considerations include:
- Keep reducers as close to the pump as straight run requirements will allow. Use eccentric reducers, flat side up, on most pump suction lines.
- Use long radius elbows, and minimize the number of elbows.
- Install temporary strainers during startup if permanent strainers are not used.
Here are a couple of don’ts:
- Do not have high points in pump suction piping. This will prevent vapor collection in the line.
- Do not mount valves directly on pump flanges. Besides disrupting smooth flow, this will make it difficult to perform maintenance on the pump.
Pump Discharge Piping
Discharge piping is usually one or two line sizes larger than the pump nozzle. A check valve and block valve are located near the pump discharge nozzle. If the discharge line is two line sizes larger than the pump nozzle, the check valve and block valve should be one size larger than the pump nozzle. Make sure to install the check valve per the manufacturer’s recommendations.
Other discharge piping guidelines include:
- Keep reducers as close to the pump as possible.
- If the flow must be controlled, install the control valve on the discharge side, never on the suction side.
- Provide a drain between the check valve and the block valve.
- Provide pressure gauge piping with a bleed between the pump nozzle and the check valve.
- Avoid pockets where air or vapors can accumulate.
- Do not mount valves directly on pump flanges. They will make it difficult to perform maintenance on the pump.
Pumps are important for keeping every part of an operation running. Next time, we will look at layout considerations for piping and pipe racks.
Matrix Technologies is one of the largest independent process design, power systems engineering, industrial automation engineering, and manufacturing operations management companies in North America. To learn more about our manufacturing operations management capabilities and manufacturing process control solutions, contact Scott Saneholtz, PE, Senior Manager Process Solutions Department.
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