Issues regarding the return pipe of the pump
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Question 1: It is not clear what type of pumps require a return pipe ? Question 2: Determine whether this design is reasonable: The chemical centrifugal pump has an inlet diameter of DN125 and an outlet diameter of DN80; its flow rate is 160, head is 32, and power consumption is 22 KW. I have used a DN32 return pipe, with butterfly valves installed at both the inlet and outlet, as well as on the return pipe. Is this appropriate? ? ? ?
There are 6 types of protection wires for pumps: heating pump wire, bypass wire, balance wire, anti-condensation wire, safety valve wire, and low-flow wire. I’m not sure if by ‘return line’ you mean a low-flow line. When the operating flow rate of the pump is 30% below its rated flow rate, the pump operates at low efficiency, which causes the liquid temperature at the inlet to rise and the vapor pressure to increase, making cavitation more likely to occur. To prevent cavitation, a low-flow line should be provided to allow the pump to operate properly at its minimum flow rate. Check whether the pipe diameter is appropriate based on the flow rate; butterfly valves do not have good sealing properties, so gate valves are recommended.
1. If the minimum operating flow rate of the pump is not lower than 20-30% of the pump’s rated flow rate, then there is no need to install a return valve. 2. Butterfly valves with a DN32 diameter are generally not produced; since the requirements regarding resistance loss for the return pipe are not strict, a globe valve can be used – it provides good sealing and is also cheaper. A pipe with a DN32 diameter is sufficient to meet the requirements
The pump has 6 types of protection pipelines: 1) Warm pump line – when transporting high-temperature oils, a DN20-25 warm pump line is installed in the presence of a backup pump； 2) Low-flow line – When the pump’s operating flow rate is below 30% of its rated flow rate, a low-flow line should be provided to allow the pump to operate at its minimum flow rate ； 3) Balance line – Used to convey liquids with a saturated vapor pressure at room temperature that is higher than atmospheric pressure, or liquids in the bubble point state; it is installed to prevent vaporization of the liquid within the pump or the entry of bubbles into the pump, which could cause cavitation ； 4) Bypass line – used for the trial operation of the pump, or when the main outlet valve is closed under abnormal operating conditions, to allow the pump to continue running, or in situations where the pressure difference before and after the valve is very high ； 5) Anti-coagulation line – used for transporting liquids that tend to solidify at room temperature. 6) Safety valve line – A safety valve line is provided on the outlet side of the positive displacement pump; when the pressure at the outlet exceeds a certain level, the liquid returns to the pump’s inlet pipe. What the original poster mentioned might refer to a low-flow protection pipeline, which generally uses a stop valve along with a flow-limiting orifice plate.
I understand it should be a pipeline that runs from the pump outlet, through a branch pipe, back to the storage tank, used for regulating pressure and flow rate. For DN32 pipes, ball valves will work fine. But is using a DN32 valve for an outlet with a diameter of DN80 a bit too small?
It is hoped that safety factors will be taken into account to increase the diameter of the return pipe! If it is a storage tank, it is recommended to use a DN80 valve for the return pipeline
Hehe, I’d like to ask everyone about the performance of the minimum flow valves used for backflow control in pumps manufactured by various pump and valve factories