If we start the pump with discharge valve closed, it means there no discharge head and minimum resistance to the pump and so current drawn is minimum. Although the current taken during startup of motor is more than normal, but by closing the discharge valve of centrifugal pump we can avoid extra load act on the pump.
When do you open the discharge valve on a centrifugal pump?
The discharge valves can be opened when there is a check valve. If there is pressure on the discharge side of the centrifugal pump without a check valve when starting, the discharge valve should be closed. Thinking from another aspect, if there are pressures at the discharge end of the pump, it may flow back into the pump before starting.
How to control the flow of a centrifugal pump?
If you need to control the flow, use a valve on the discharge side of the pump, never use a valve on the suction side for this purpose. This is an excellent treatment of the types of control systems for a centrifugal pump by Walter Driedger. And also this article by the same author on how to control positive displacement pumps. 9.
Why does the current increase when the discharge valve is open?
>As you know,the current will be high during the starting of any motor. If you start the pump with discharge valve open, the discharge head will act on the pump ie, more resistance, so the motor has to give more starting torque to the pump which means more current is drawn by the motor.
What happens when a water pump valve is open or closed?
If the valve is open and the pump is switched on, there is a sudden power load corresponding to the flow rate. If the valve is closed (zero flow) the power load is minimum ie minimum current.
Why we need to start the pump when the discharge valve is close?
A closed discharge valve at startup or shutdown also prevents backflow from any static discharge head. Pumps that require less shut-off power and torque than at normal flow conditions are usually started against a closed discharge valve.
What happens if discharge valve of centrifugal pump is closed?
If the discharge valve is closed and there is no other flow path available to the pump, the impeller will churn the same volume of water as it rotates in the pump casing. This will increase the temperature of the liquid (due to friction) in the pump casing to the point that it will flash to vapor.
What will happen while starting if discharge valve of reciprocating pump is closed?
If we start the pump with discharge valve closed, it means there no discharge head and minimum resistance to the pump and so current drawn is minimum. Although the current taken during startup of motor is more than normal, but by closing the discharge valve of centrifugal pump we can avoid extra load act on the pump.
Which pump will be damaged if discharge valve is closed?
A dead-head is caused when a centrifugal pump operates with no flow through the pump due to a closed discharge valve or blockage in the line. The pump is forced to circulate the pumped medium, causing the temperature to continually rise.
What happens if the pump delivery valve is completely closed during running condition?
The pump speed will actually go up. This sounds counter intuitive until your realize that you are no longer accelerating or moving material so the energy absorbed by the system goes down. 2. The shearing on the material goes up and the liquid will heat up more than it would if the pump was allowed to operate normally.
Should the discharge valve be opened before starting a positive displacement pump?
Precautions Prior to Starting Pump Verify that all suction and discharge valves are open before starting the pump. Prime the pump and jog the motor to check the rotation.
When first starting a centrifugal pump delivery valve is kept?
The delivery valve connects the pump outlet and the delivery pipe. It remains closed before the pump is switched on. When the pump builds up its pressure, it is opened and can be used to control or vary the discharge.
Why centrifugal pump has no relief valve?
Because maximum pressure with the discharge closed is only moderately above working pressure, a relief valve is not necessary for a centrifugal pump.
What is pump discharge valve?
Valves on a pump control the flow of liquid through a pump. These help to regulate pressure within a pump and prevent against possible breakage. Any pump should have two valves attached; one at the inlet, or suction, and the other at the outlet, or discharge area.
What is discharge valve?
Discharge Valves are devices that make it possible to monitor and control the flow of a substance from a source and through some type of circulation system.
Does partially closing a valve increase pressure?
The mains shut off valve controls the overall flow of water into your home. However, if the shut-off valve is even partially closed, it can cause a reduction in the mains water pressure to your home.
Why are centrifugal pumps not recommended?
That’s the reason for certain applications Centrifugal Pumps are NOT recommended but people still use them due to lack of knowledge.
What happens when a centrifugal pump is dead headed?
Dead heading (closing the delivery or exit valve) of a centrifugal pump will cause a few things to happen. 1. The pump speed will actually go up. This sounds counter intuitive until your realize that you are no longer accelerating or moving material so the energy absorbed by the system goes down.
What happens if there is no liquid in the pump?
If delivery valve means the supply/suction side of the pump, and there is liquid in the pump, it will indeed cavitate and soon damage the rotor/runner and probably the scroll case. If there is no liquid in the pump it probably will not damage the rotor or case but the seal will soon overheat and be damaged.
What happens if a pump is delivered with liquid?
If delivery valve means the outlet/discharge side of the pump and the pump is solidly filled with liquid, damage to the parts will be delayed until the fluid boils, then cavitation will damage the parts. Allowing even a tiny amount of water to pass through the pump and valve will cool it enough to prevent damage.
Does the electrical load on a motor go down?
The electrical load on the motor will definitely go down. The mechanical load on the pump shaft will go way up. (not good) Where most people get confused on this subject is that closing the discharge valve will increase pressure to shut off head.
Do low specific speed pumps need to be primed?
Properly primed Low Specific speed pumps operating at full speed requires less power during start-up when Discharge Valve is partially closed. It is advantageous, but not necessary, in fact most of the times mixed flow and axial flow pumps require higher input power with discharge valve closed as against the power required against closed discharge valve startup.
What is the main criteria which determines whether the application requires a centrifugal pump or a positive displacement?
Viscosity is the main criteria which determines whether the application requires a centrifugal pump or a positive displacement pump. Centrifugal pumps can pump viscous fluids however the performance is adversely affected. If your fluid is over 400 cSt (centiStokes) in viscosity consider using a positive displacement pump.
What is the best efficiency point for centrifugal pumps?
Most centrifugal pumps should not be used at a flow rate less than 50% of the B.E.P. (best efficiency point) flow rate without a recirculation line. ( What is the B.E.P.?) If your system requires a flow rate of 50% or less then use a recirculation line to increase the flow through the pump keeping the flow low in the system, or install a variable speed drive.
How to diagnose pump system problems?
Use pressure gauges. Make sure your pump has a pressure gauge on the discharge side close to the outlet of the pump this will help you diagnose pump system problems. It is also useful to have a pressure gauge on the suction side, the difference in pressure is proportional to the total head.
How to stop a pump from making a noise?
To remedy, shut the pump down and open the vent valve to remove the air. If the pump is excessively noisy do not automatically assume that the problem is cavitation, air in the pump creates vibration and noise. Cavitation produces a distinct noise similar to gravel in a cement mixer. If you have never heard the sound of cavitation here's a recording of it in WAV format, courtesy of my friend Normand Chabot, water hammer specialist here in Montreal.
What is the relationship between flow and pressure?
1. Flow and pressure relationship of a pump. When the flow increases, the discharge pressure of the pump decreases, and when the flow decreases the discharge pressure increases (ref. tutorial2.htm ). 2. Do not let a pump run at zero flow. Do not let a centrifugal pump operate for long periods of time at zero flow.
What type of pump should I use for deep wells?
7. Use a multi-stage turbine pump for deep wells
What valves should be used at the pump?
Gate valves at the pump suction and discharge should be used as these offer no resistance to flow and can provide a tight shut-off. Butterfly valves are often used but they do provide some resistance and their presence in the flow stream can potentially be a source of hang-ups which would be critical at the suction. They do close faster than gate valves but are not as leak proof.