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Design of inlet and outlet pipeline of pump

Cavitation phenomenon: when the static pressure of the liquid entering the first stage impeller of the pump is lower than or equal to the saturated vapor pressure at this temperature, the liquid vaporizes and generates vapor bubbles. With the liquid flowing into the higher pressure, the vapor bubble suddenly condenses, and the surrounding liquid quickly concentrates, resulting in hydraulic impact. This kind of vaporization and condensation produces the phenomenon of pump erosion, vibration and performance degradation, which is usually called cavitation phenomenon.

20201028112854 71604 - Design of inlet and outlet pipeline of pump

Pump installation sequence: technical preparation → foundation acceptance → open box inspection → equipment hoisting and positioning → initial leveling and alignment → secondary grouting → fine leveling and alignment → secondary grouting → pump and motor coupling alignment → process pipeline installation → alignment and stress review → commissioning preparation, single commissioning → load commissioning → handover and acceptance.
Note: the inside of the pipe connected with the equipment should be cleaned up. The fixed welding joint should be away from the equipment. No additional force is allowed on the equipment. The inlet and outlet of the equipment shall be provided with temporary blind plate, which can be removed after the pipeline is cleaned. The flange spacing should be the minimum distance that can be put into the gasket smoothly. When the pipe is finally connected, its radial displacement shall be monitored with a dial indicator on the coupling. When the speed is less than 6000 rpm, the displacement is less than 0.05 mm. When the speed is more than 6000rpm, the displacement is ≤ 0.02mm. Otherwise, adjust the pipe.
When the pump inlet pipe system has a reducer, the eccentric reducer is used to prevent gas accumulation at the pipe diameter ≥ DN65. The installation method of the reducer is shown in the figure, that is, when the front elbow of the inlet flange is downward, the top of the reducing pipe is flat; when the elbow is upward, the reducing pipe bottom is flat.

20201028225237 84385 - Design of inlet and outlet pipeline of pump

Installation method of reducer

On site installation display: media from top to bottom

20201028225549 31759 - Design of inlet and outlet pipeline of pump

On site installation display: media from bottom to top

20201028225832 69680 - Design of inlet and outlet pipeline of pump

The straight pipe section above the inlet diameter of the pump, so as to make the liquid enter into the pump smoothly, and avoid the bias flow and rotary flow, which may cause the vibration and noise of the pump.
When the piping of double suction pump is upper suction, it is unnecessary to consider the straight pipe section required on the suction inlet. The vertical pipe can be directly connected with the suction pipe orifice through elbow and reducer, and it is required to be as short as possible.
When the inlet and outlet of the pump are in the same vertical plane, eccentric reducer or two 45 ° elbows can be used to increase the distance between inlet and outlet pipes in order to facilitate the installation of valves.

20201028230223 36098 - Design of inlet and outlet pipeline of pump

Y-type filter

20201028230239 82884 - Design of inlet and outlet pipeline of pump

Cone filter

The outlet pipeline of the pump should be flexible, especially under the condition of high temperature and high pressure. The geometric shape of the pipeline should be determined according to the size of the thermal stress after stress analysis.
Pump outlet and deep protection pipeline design:
Pump outlet should not be directly connected with elbow. Pump outlet between the cut-off valve and check valve with a drain valve. The pump outlet pressure gauge is installed on the short joint between the pump port and the check valve, and can also be installed on the outlet reducer. The nozzle of the pressure gauge shall have a root valve, and the head of the pressure gauge shall face the operating surface.
Pre hot wire: when the medium temperature of the pre hot wire is higher than 200 ℃, in order to avoid the high temperature liquid pouring into the pump to be operated when the pump is switched over, the pump body and impeller will be damaged or deformed due to uneven heating, causing the fixed part and rotating part to get stuck. Therefore, it is necessary to set up the pre hot wire to keep the stopped pump in the state of waiting to start, so as to switch at any time.

  • Pump protection line – small flow line: when the pump’s working flow is less than 30% of the pump’s rated flow, it will produce a force perpendicular to the axial direction – radial thrust. Moreover, as the pump operates under low efficiency, the liquid temperature and steam pressure at the inlet are increased, and cavitation is easy to occur. In order to prevent cavitation, a small flow line should be set for normal operation of the pump at the lowest flow rate.
  • Pump protection pipeline balance line: for the liquid conveying saturated vapor pressure and high dry atmospheric pressure at normal temperature in bubble point state, in order to prevent the liquid entering the pump from producing steam or bubble entering the pump to cause cavitation, it is generally appropriate to set the balance line. The balance line is the gas phase section from the pump inlet to the suction tank (tower).
  • Pump protection pipeline bypass line: when starting a high lift pump, the outlet valve is pressed too much unilaterally and is not easy to open. If forced to open, the valve stem and valve seat will be damaged. The bypass line with restriction orifice plate is set in front of and behind the outlet valve, which can be opened easily. At the same time, the bypass line can also reduce pipeline vibration and noise.
  • Protection pipeline of pump — anti condensation line: when conveying liquid with high pour point or high freezing point solidified at normal temperature, its standby pump and pipeline shall be provided with anti condensation line to avoid blockage of standby pump and pipeline. Generally, two DN20 anti condensation lines are set. One of them is connected from the pump outlet shut-off valve to the front of the check valve (used when the pump is standby). The other anti condensation line is connected from the pump outlet shut-off valve to the front of the pump inlet shut-off valve (used in the maintenance of the standby pump). Open the corresponding anti condensation valve to ensure that the fluid in the pipeline does not condense.
  • Pump protection pipeline safety valve line: for electric reciprocating pump and rotary pump, a safety valve should be set at the outlet side. When the outlet pressure exceeds the constant pressure value, the safety valve will start to trip and the fluid will return to the inlet side. The pipeline should be arranged as compact as possible without affecting the operation.

Source: China Pipe Fitting Manufacturer – Yaang Pipe Industry (

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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