Selection of water pump pipelines and accessories

This is the typical process for the pump; please refer to it. I. Pump suction pipeline layout: 1. Pipe diameter – The diameter of the inlet pipe for a centrifugal pump should be 1–2 sizes larger than the diameter of the flow entering the pump ； The inlet diameter of the reciprocating pump should be 1–3 sizes larger than the inlet diameter, after which it should be equal to it ； In short, hydraulic calculations are required to ensure that the necessary net positive suction head is met for the pump. 2. Slope of the pipeline: If the pump’s inlet and outlet pipelines may be filled with gas, and the liquid suction device is located above the pump, then the inlet pipeline should slope from the liquid suction device toward the pump; a slope of at least 1:6 is recommended. 3. Isolation valve: To facilitate maintenance and startup, an isolation valve should be installed as close as possible to the pump inlet, with a diameter that matches that of the pipe. To save on valve investment, when the suction pipe diameter is two sizes larger than the inlet pipe diameter, a valve one size larger than the inlet pipe diameter can be used, but it is necessary to verify the net positive suction head. If the system has only one pump, the pressure rating of the isolation valve should be the same as that of the inlet pipe; if there are two or more pumps, then the rating of the isolation valve and the piping connecting it to the pumps should be at least 3/4 of the maximum outlet pressure at normal operating temperatures. 4. Filters: Permanent filters should be installed on pumps with small clearance, such as screw pumps, gear pumps, plunger pumps, etc. One is installed on each unit, located between the cut-off valve and the pump inlet. Unless the fluid to be pumped is dirty or special requirements apply, centrifugal pumps generally do not have permanent filters, but a temporary filter for startup is required. When the diameter is 40 or greater, a permanent filter can also be installed; Y-type filters are commonly used, and they are installed just downstream of the shut-off valve on the pump’s suction pipeline. 5. Buffer tank: When the net positive suction head of the reciprocating pump is sufficient to meet the requirements, a buffer tank can be installed on the inlet pipeline. II. Pump discharge pipeline layout: 1. Isolation valve – An isolation valve should be installed at the pump outlet, and the diameter of this valve should match that of the pipeline. If the pipe diameter is one size or even two sizes larger than the pump’s outlet diameter, then the valve can be one size smaller than the pipe diameter. For centrifugal pumps with an inlet-outlet pressure difference greater than 4.0 Mpa, it is advisable to install twin shut-off valves in series. 2. Check valve: Positive displacement pumps usually do not have check valves. Each centrifugal pump or vortex pump shall be equipped with a check valve between its pump outlet and the shut-off valve, with a diameter equal to that of the shut-off valve. When the pump outlet pipeline is branched, it is advisable to install a check valve on the pump outlet bus. For centrifugal pumps with an inlet-outlet pressure difference greater than 4.0 Mpa, it is advisable to install twin shut-off valves in series. 3. Pressure relief valve: A safety valve should be installed between the outlet of each reciprocating pump and rotor pump and the first valve; if the pump is equipped with its own safety valve, then an additional one is not necessary. A pressure relief valve is generally not installed at the outlet of a steam reciprocating pump, but when the pump gets out of control and the pressure exceeds what the pump body can withstand, or when the pump pressure has a significant impact on the downstream system, a pressure relief valve should be installed at the pump outlet. Safety valves should be installed in other types of pumps where an increase in pressure due to the closure of the outlet valve could damage the pipes or equipment. 4. Pressure gauge: A pressure gauge should be installed at the outlet of each pump, on the straight section of pipeline between the pump and the first valve at the outlet. 5. Buffer tank: Buffer tanks must be installed on the pipelines of reciprocating pumps in the following situations: (1) To improve the accuracy of measurement and reduce the amplitude of flow pulses, buffer tanks should be placed upstream of the flow meter for single-cylinder or double-cylinder single-acting pumps; for double-cylinder double-acting and three-cylinder pumps, buffer tanks are only required on the main inlet and outlet pipes. (2) To reduce vibration in high-pressure pipelines, buffer tanks should be installed. When P ≥ 3.5 Mpa, it is necessary to discuss with the pump designer whether to install a buffer tank. (3) Pumps are used in hydraulic systems; to prevent hydraulic pulsations from causing unstable system operation, a buffer tank should be installed. III. Venting and Draining Pipes 1. Venting: Except for pumps that discharge air on their own, vent pipes for startup purposes must be provided. To prevent air blockage, an operational vent pipe should be installed on the inlet pipeline. The venting from the vacuum system should all be returned to the gas space of the liquid absorption equipment. Pumps for transporting liquefied petroleum gas are equipped with a vent pipe leading to a sealed system on the pump inlet pipeline. When transporting materials such as asphalt, it is necessary to frequently vent the material from the system; the venting pipes should be connected back to the liquid absorption equipment, and heating pipes should be installed. 2. Drain valve: The casing of horizontal pumps should be equipped with a drain valve. If the material between the inlet and outlet shut-off valves cannot be completely drained through the pump, a drain valve should be installed on the pipeline; on the outlet pipeline of the centrifugal pump, a drain valve should be placed between the check valve and the shut-off valve. IV. Other Piping 1. Low-flow Protection Piping: If a centrifugal pump might operate at a flow rate below its minimum allowable value, a low-flow protection piping system should be installed to allow a portion of the fluid to return from the pump’s discharge outlet back into the container at the pump’s inlet. When the pump is operated for short periods at a flow rate of less than 20% of its rated value, a bypass with a flow-limiting orifice plate (along with a stop valve or control valve) should be installed ； Its flow rate should be at least 20% of the rated flow rate; if flashing may occur when the fluid passes through the bypass orifice plate, appropriate cooling measures should be considered. If a centrifugal pump operates for extended periods at a flow rate below 30% of its rated value, an orifice plate control bypass should be installed, with this bypass connected to the pump’s suction equipment. 2. Heat pumps and anti-freezing pipelines: When the temperature of the material transported by a centrifugal pump exceeds 200°C, anti-freezing and heat pump pipelines are required. A small amount of material is drawn out from the operating pump through a discharge pipeline, flows through the body of the standby pump, and then returns to the pump inlet, keeping the pump in a hot standby state. This prevents the medium in the standby pump as well as in the suction and discharge pipelines from freezing, thereby ensuring proper operation of the heat pump and facilitating its startup. In the diagram, pipe A is the anti-freezing and condensation pipe for the inlet and outlet; it can be used together during shutdowns for pipeline cleaning ； Pipe B is the pipeline for starting the heat pump; when the diameter of the drainage pipe is less than DN80, Pipe B can be omitted, and opening the outlet valve slightly can be used as a substitute. The bypass flow is about 3-5% of the normal flow. If the temperature is below the freezing point of the material, a heating pump bypass must be installed to prevent the material from freezing inside the pump. In addition, an anti-freezing bypass should be provided between the pump’s inlet and outlet; the connection point between this bypass and the main pipeline should be as close as possible to the shut-off valve, in order to avoid the formation of dead zones. The anticoagulation bypass is heated using steam or electric heating. 3. Balance pipes: For pumps that transport liquids at normal temperature with a saturation vapor pressure higher than atmospheric pressure or in a flashing state, especially vertical pumps, balance pipes should be installed between the pump’s inlet and outlet and the shut-off valves, to prevent steam from entering the pump and causing cavitation. The balance tube should be led out as close as possible to the pump inlet, returning to the gas space of the suction device. Isolation valves should be installed on the balance pipes. 4. High pressure in the pipes: The pressure difference on both sides of the outlet shut-off valve of high-head pumps is relatively large, resulting in significant one-way pressure on the valve discs. Especially when the large valve cannot be opened, a DN20 bypass should be installed in front of and behind the valve. Before opening the main valve, the bypass valve should be opened first to balance the pressures on both sides of the main valve, thereby enabling its smooth opening.

I would like to ask what precision is generally chosen for the temporary filter at the inlet of a centrifugal pump? Thank you

Thank you for the advice! I just found out today that the connection methods for the two ports of the pump are different