Why is there a backpressure valve on the outlet pipeline of the metering pump?
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The flow rate of a metering pump is regulated by its stroke and does not change as the resistance in the downstream pipeline changes. So why is a back pressure valve installed at its outlet?
The backpressure valve can reduce overpressure in downstream equipment, protecting it
That’s not quite right! The outlet pressure of the metering pump is entirely determined by the pressure in the downstream pipes and equipment; as long as the downstream equipment is not under excessive pressure, the outlet pressure of the metering pump will not exceed a certain level.
I’ve seen many metering pumps with wires running from the inlet, outlet, and safety valve as well
The purpose of a safety valve is to prevent overpressure caused by blockages downstream.
You can understand why it is installed by considering the function of the back pressure valve (the following is from Baidu Baike): 1. The check valve on the outlet pipe prevents liquid from flowing back, while the back pressure valve ensures a constant pressure at the pump’s outlet. 2. It can be used as a safety valve in systems with less stringent requirements. 3. Used in combination with pulsation dampers to reduce the damage caused by water hammer to the system, lower the peak values of flow velocity fluctuations, and protect pipelines, elbows, and connections from the effects of pressure fluctuations. 4. Create a favorable working environment for the metering pump and improve its performance. 5. Ensure the stability of the water flow rate output by the pump; since the flow rate of some pumps varies significantly with pressure, a backpressure valve can be installed at the pump’s outlet to stabilize its output flow. In such cases, the pressure of the backpressure valve is usually set to the actual operating pressure of the pump or slightly lower than that pressure. 6. It can maintain the required pressure in the pipelines or equipment containers, ensuring that the pump can deliver flow normally even when the pressure is unstable. 7. At the pump’s outlet, self-priming or siphoning phenomena often occur due to gravity or other factors. A back pressure valve can reduce the fluctuations in flow rate and pressure caused by siphoning; in such cases, a pressure value that is greater than the liquid’s own pressure is sufficient. For example, to prevent the liquid in a tank with a liquid level of 2 meters from flowing out on its own, a back pressure valve with a pressure of more than 0.02 MPa can be used, although 0.1 MPa is usually sufficient.
A metering pump belongs to the category of positive-displacement pumps, and its outlet cannot build up pressure. When the outlet is overpressured, the material returns to the tank via the backpressure line. Once, at our facility, the backpressure manual valve of the foam pump wasn’t opened, and when the pump was started, it blew the valve disc of the check valve away.
A backpressure valve is not used in the return pipeline; it is the safety valve that is used in that pipeline.
1. To prevent liquids from flowing by gravity (or through siphoning). 2. To stabilize the flow rate of a pump; in cases where the flow rate of certain pumps changes significantly with pressure, a backpressure valve can be installed at the pump’s outlet to maintain a constant output flow rate