What happens if you dead head a positive displacement pump?
Positive displacement pumps, which are what gear pumps are, should not be deadheaded, as they will break immediately. The exception to this for gear pumps is when the viscosity is so low that the fluid slipping backwards through the pump is actually relieving it (giving the fluid somewhere to go).
What is shut-off head in pump?
Shutoff head is the head a pump will develop when operating against a closed discharge valve. The point where the left side a pump performance curve intersects with the Y-axis is the shutoff condition. The head corresponding to that point will be produced when the pump is producing no flow.
What happens if you close the discharge valve of a positive displacement pump?
A positive displacement pump operating against a closed discharge valve will continue to produce flow until the pressure in the discharge line has increased until the line bursts or the pump is severely damaged – or both.
Why is it not recommended to close a discharge valve in positive displacement valve?
A positive displacement pump should not operate against a closed valve on the discharge side of the pump because it has no shutoff head like centrifugal pumps do; a positive displacement pump operating against a closed discharge valve continues to produce flow, and the pressure in the discharge line increases until the …
What will happen if the pump flow output of a positive displacement pump gets blocked?
a Positive displacement pumps. Another feature of PD pumps is that, if the line for any reason becomes blocked, they simply continue forcing high-pressure fluid into the line and eventually break something if a precautionary rupture system has not been installed.
Is it OK to deadhead a centrifugal pump?
When a centrifugal pump is dead-heading, it can lead to explosions, due to the energy being put into the liquid in the pump. Hydraulic overpressure and possible chemical reactions in the pump can also be caused by the overexertion of pressure.
Why is shut off head important?
The maximum head (shut-off head) is achieved at a flow rate of zero. Increasing flow rate introduces friction into the system as the liquid travels along the pipes from the suction tank to the pump and from the pump into the discharge pipe. This friction reduces the amount of total head that the pump can produce.
Which is positive displacement pump?
A positive displacement pump makes a fluid move by trapping a fixed amount of the fluid and forcing (displacing) that trapped volume into a discharge pipe or discharge system. Liquid flows into the pump as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses.
What would happen if the discharge valve is closed for a positive displacement pump B centrifugal pump Why?
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. The vapor can interrupt the cooling flow to the pump’s packing and bearings, causing excessive wear and heat.
Do positive displacement pumps Cavitate?
Cavitation is a potentially damaging effect that occurs when the pressure of a liquid drops below its saturated vapour pressure. Cavitation can also occur in positive displacement pumps such as gear pumps and plunger pumps.
Can a positive displacement pump run backwards?
The liquid is carried between the gear teeth and the casing to the opposite side of the pump. The meshing of the gears forces the liquid into the outlet line. By reversing rotation, the function of the nozzles will be reversed and the pump will be able to pump ‘backwards’.
How one would protect a positive displacement pump?
Positive displacement pumps are normally fitted with relief valves on the upstream side of their discharge valves to protect the pump and its discharge piping from over pressurization.
Can a positive displacement pump operate against closed valves?
A Positive Displacement Pump must never operate against closed valves on the discharge side of the pump – it has no shut-off head like Centrifugal Pumps.
What is the shut off head of a pump?
This is known as the “shut-off head”, it’s the amount of head a pump can produce at zero flow. To choose your required pump, you need to know two things: the total head and what flow rate you require. As you might expect, these two quantities are related. The maximum head (shut-off head) is achieved at a flow rate of zero.
What causes a pump to shut off at zero flow?
The pump is working, but the force of gravity causes the water’s rise in the vertical discharge pipe to stop and the net flow stops. This is known as the “shut-off head”, it’s the amount of head a pump can produce at zero flow. To choose your required pump, you need to know two things: the total head and what flow rate you require.
When do you use the positive displacement principle?
The positive displacement principle applies whether the pump is a rotary lobe pump progressing cavity pump rotary gear pump piston pump diaphragm pump screw pump gear pump vane pump regenerative (peripheral) pump peristaltic