Why install a foot valve under the inlet pipe of a centrifugal pump?From the point of view of energy

Unfavourable. If you don't install a bottom valve, once the pump stops, the water in the suction pipe will leak out, and you have to refill the water. From the point of view of energy saving, this is very unfavorable to energy saving, because the head loss coefficient of the foot valve is very large, and the simple point is that its resistance is very large and it consumes energy, so it is very unfavorable to energy saving.

The new products are a little better, but there is still a lot of resistance. If the negative suction type is used (the elevation of the pump is lower than the elevation of the suction surface), there is no need for a foot valve.

A pump is a piece of machinery that transports or pressurizes a fluid. It transfers the mechanical energy or other external energy of the prime mover to the liquid, which increases the energy of the liquid. The pump is mainly used to transport liquids such as water, oil, acid and alkali, emulsion, suspension emulsion and liquid metal, and can also convey liquid, gas mixture and liquid containing suspended solids.

Pumps can usually be divided into three categories: positive displacement pumps, power pumps, and other types of pumps according to their working principle. In addition to classifying by working principle, it can also be classified and named in other ways.

For example, according to the driving method, it can be divided into electric pump and water wheel pumpAccording to the structure, it can be divided into single-stage pump and multi-stage pump;According to the use, it can be divided into boiler feed pump and metering pumpAccording to the nature of the conveyed liquid, it can be divided into water pump, oil pump and mud pump. According to the shaft structure, it can be divided into linear pump and traditional pump. The water pump can only convey fluid-based logistics, not solids.

The function of installing a foot valve under the inlet pipe of the centrifugal pump is to prevent the water in the pumping pipe from flowing out when the pump stops working. It has nothing to do with energy saving.

The pump should fill the pumping pipe with water before working. When the pump is driven by power, the pump shaft rotates at high speed. A low-pressure zone is formed in the pump.

Water from a river or well is pressed into the inlet pipe under atmospheric pressure. The water pump impeller flicks the water from the pump body to the outlet pipe. In this way, the water is pumped up continuously.

If you don't install it, you have to fill the suction pipe every time you pump water, otherwise you can't pump out the water, which has nothing to do with energy saving, and has to do with efficiency.

Unreasonable, the installation of valves on the inlet pipeline will increase the resistance on the inlet pipeline, which is easy to cause cavitation. Centrifugal pump.

It is to use the rotation of the impeller to make the water centrifugal motion to work. Before the pump starts, the pump casing and suction pipe must be filled with water, and then the motor is started to make the pump shaft drive the impeller and the water to do high-speed rotation movement, and the water undergoes centrifugal movement, which is thrown to the outer edge of the impeller and flows into the pressurized water pipeline of the pump through the flow channel of the snail pump casing. A centrifugal pump is a vane pump that relies on a rotating impeller during rotation, and the blades will have mechanical energy due to the interaction between the blades and the liquid.

Transfer to the liquid, so that the pressure of the liquid can be increased, to achieve the purpose of transporting the liquid. There are four points to pay attention to when starting the centrifugal pump: There is a limit to the head generated by the centrifugal pump at a certain speed when the shroud is removed.

The operating point flow and shaft power depend on the condition of the unit system connected to the pump (differential position, differential pressure and loss of line). The head varies with the flow rate. The work is stable, the conveying is continuous, and the flow and pressure are pulsation-free.

Generally, there is no self-priming ability, and the pump needs to be filled with liquid or the pipeline pumped into a vacuum before it can start working. Centrifugal pumps, vortex pumps and axial flow pumps are started with the discharge line valve closed.

Activate with the valve fully open to reduce the starting power. Because centrifugal pumps rely on the centrifugal force of the impeller.

The suction force that forms a vacuum lifts the water, so when the centrifugal pump starts, the gate valve must be closed and the water must be filled first. If the water level exceeds the impeller part, the air in the centrifugal pump is discharged before it can be started. After starting, a vacuum is formed around the impeller to suck the water upwards, and its gate valve can automatically open to lift the water.

Therefore, the gate valve must be closed first.

The control valve should not be installed at the inlet pipe of the centrifugal pump.

Because the throttling at the inlet pipe of the centrifugal pump will cause cavitation (vapor phase generation) before the medium enters the pump, resulting in damage to the pump blades;

In addition, from the perspective of regulation, the centrifugal pump itself has a certain ability to stabilize the pump outlet pressure (flow) within a certain range, which will seriously offset the regulating effect of the regulating valve, and when it exceeds this range, the pump outlet pressure (flow) will change sharply, so that the actual range of the regulating valve can be greatly reduced.

The main working principle of centrifugal pump:

1) The impeller is driven to rotate by the pump shaft, and the work is done on the fluid located between the blades, and the fluid is thrown to the periphery by centrifugal action. When the fluid reaches the outer periphery of the impeller, the flow rate is very high.

2) The pump casing collects the liquid that is thrown from between the blades, and these liquids flow in the shell in the direction of the gradual expansion of the volute-shaped stool road, so that the kinetic energy of the fluid is converted into static pressure energy and the energy loss is reduced. Therefore, the role of the pump casing is not only to collect liquid, it is also an energy conversion device.

3) Liquid suction principle: relying on the high-speed rotation of the impeller, the liquid in the center of the impeller is forced to be thrown away at a high speed, so as to form a low pressure in the center of the impeller, and the liquid in the low groove is continuously sucked up.

4) Guide wheels are installed around the outer periphery of the impeller to make the liquid energy conversion efficiency in the pump high. The guide pulley is a fixed ring with blades located on the outer periphery of the impeller. The bending direction of these blades is opposite to the bending direction of the impeller blades, and its bending angle is just adapted to the direction of the liquid flowing out of the impeller, guiding the liquid to change direction smoothly in the pump casing channel, so that the energy loss is minimized, and the conversion of dynamic pressure energy into static pressure energy is efficient.

5) Balance holes in the rear cover plate eliminate axial thrust. The pressure of the liquid leaving the perimeter of the impeller is already high, and some of it will seep into the back of the impeller cover, and the liquid inlet on the front side of the impeller is at low pressure, resulting in an axial thrust that pushes the impeller towards the inlet side of the pump.

6) The shaft sealing device ensures the normal and efficient operation of the centrifugal pump. If the annular gap between the centrifugal pump is not sealed or not well sealed, the outside air will penetrate into the low-pressure area of the center of the impeller, so that the flow rate and efficiency of the pump will decrease.

Unreasonable is easy to produce throttling loss, pressure loss, pressure reduction, and cavitation.

Unreasonable, because the water is transported from the pool or tank to the pump by the pressure difference between the atmospheric pressure on the liquid surface and the vacuum at the pump inlet, if the valve is installed on the inlet pipe, the resistance of this section of the pipeline will be increased, which may cause the liquid sucked in the pump casing to vaporize due to the decrease in pressure at the suction inlet, resulting in the phenomenon of "cavitation".

Imported Brown valves must be installed.

Reasonable, how to debug and overhaul without valves.

Valves with relatively large CV values are generally installed on the inlet.

A one-way foot valve is installed at the end of the suction pipe of a centrifugal pump to prevent "cavitation". （）

a.That's right. b.The wrong grinding is a mistake.

Correct Answer: Blind and false.

Depending on the situation, it is impossible for the pump to be free from failure, and in order to facilitate the maintenance of the pump, valves need to be installed at the front and rear to prevent the leakage of liquid in the piping system.

It is possible to install a foot valve, but what is the function of other valves?

The control valve should not be installed at the inlet pipe of the centrifugal pump.

Because the throttling at the inlet pipe of the centrifugal pump will cause cavitation (vapor phase generation) before the medium enters the pump, resulting in damage to the pump blade;

In addition, from the perspective of regulation, the centrifugal pump itself has a certain ability to stabilize the pump outlet pressure (flow) within a certain range, which will seriously offset the regulating effect of the regulating valve, and when it exceeds this range, the pump outlet pressure (flow) will change sharply, so that the actual range of the regulating valve can be greatly reduced.

So although it is not absolute, it is very inappropriate for the control valve to be installed at the inlet pipe of the centrifugal pump.

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Mainly in order to reduce the resistance of the centrifugal pump when starting, the effect of the vacuum valve installed outside the inlet pipe will automatically open when the pump is stopped, minus the vacuum, when the pump is started next time, the load of the pump is in the minimum state, after the pump is normal, the vacuum valve will be automatically closed, and the vacuum is established, and the water is pressed into the inlet pipe under the action of the outside atmospheric pressure, and when it enters the pump, it is sent to the outlet of the pump by the centrifugal impeller of high-speed rotation, so as to complete the work of the pump.

Check valves and valves should be installed at the outlet of the centrifugal water pump.

I beg to differ.

It is correct to install the outlet gate at the outlet of the centrifugal pump, and the check valve should be installed near the inlet of the suction section, so that when the pump is stopped, it can ensure that the water can be stored in the pump body, and there is no need to inject water into the pump body when starting next time, and the centrifugal pump cannot pump water without water in the pump body.

Of course, installing a check valve at the outlet can also prevent the pump from reversing due to a sudden power failure.