What is deadheading a pump?

A dead-head is when a centrifugal pump operates with no flow through the pump due to a closed or blocked discharge valve. The pump will recirculate the same water, causing the water temperature to rise. The excessive heat produced can damage expensive seals and significantly reduce the life of your pump.

Why would you deadhead a pump?

A deadhead is when a centrifugal pump continues operating without any fluid flowing through the pump. Deadheading results primarily due to a closed discharge valve, line blockage, or if the check valve remains in a seated position.

Is it OK to dead head 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.

What is pump deadhead pressure?

The discharge valve is closed, leaving the pump rotating as it pushes water against a closed valve with no flow through the system. The “Dead Head” pressure is plotted in feet of head on a curve from the pump manufacturer. This verifies the pump flow potential and impeller size.

What is a dead head in plumbing?

A blockage on the discharge side of an operating pump which results in the flow reducing to zero and an increase in the discharge pressure. The energy input from the deadheaded pump increases the temperature and pressure of the fluid in the pump.

Checking Pump Performance (Dead Head Check)

Can you deadhead a gear 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).

How does a pump Cavitate?

Cavitation occurs when the liquid in a pump turns to a vapor at low pressure. It occurs because there is not enough pressure at the suction end of the pump, or insufficient Net Positive Suction Head available (NPSHa). When cavitation takes place, air bubbles are created at low pressure.

How do you find the deadhead pressure of a pump?

To find the deadhead pressure of a pump, trace the pump curve back to the far left (where the flow approaches 0 gallons per minute (gpm)) and this point on the y-axis is the deadhead pressure.

What is shut off head in centrifugal pump?

The shut-off head of a pump indicates the amount of pressure required to reach a condition where the flow rate in a vertical pipe connected to the operating pump becomes zero.

What happens when pump runs off curve?

If a pump is running out on the end of the curve it can cause cavitation inside the pump and result in premature wear of the impeller and bearings of the motor. It can also cause the motor to over amp and prematurely fail.

Can we run centrifugal pump with discharge valve 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.

Can you deadhead a diaphragm pump?

Double Diaphragm Pumps Deadhead Safely With No Product or Mechanical Damage and Seamless Restarting. Many other pumping technologies require special controls or circulation loops that allow the pump to “deadhead”.

What is priming in pumps?

What is pump priming? Priming simply means preparing or getting something ready for operation. For a centrifugal pump to work properly, you need to fill it up with water. When everything is right, a standard (non-self-priming) centrifugal pump looks like this. The pump will resume operation once the air is removed.

What is cavitation in centrifugal pump?

Cavitation occurs in centrifugal pumps when the Nett Positive Suction Head Available (NPSHa) is lower than the Nett Positive Suction Head Required (NPSHr) causing the formation and accumulation of bubbles around the impeller eye that then collapse resulting in a series of mini implosions and significant damage to both ...

What is pump runout?

Pump runout, or runout flow, is the maximum flow rate that a pump can develop. The runout conditions correspond to a very small pump head, while the flow rate is maximal. The performance curve (published by the pump manufacturer) is typically cut off at some point beyond the pump's allowable operating range (AOR).

What is churning effect in pump?

Churning in centrifugal pumps occurs when the outlet (discharge) of the pump is closed thereby causing the impeller to simply churn or “mix” the same water within the pump body. As a result, the internal temperature of the pump starts increasing which may lead to catastrophic failure of the pump.

How do I know if my pump is Cavitating?

The most common way to identify pump cavitation is through sound or vibration. There is an audible sound similar to crackling that can be heard when this is occurring. Due to the bursting of the vapor bubbles, there is increased vibration experienced by the pump, which can also be observed.

How do you stop a pump from cavitating?

What does cavitation look like?

Some describe pump cavitation as the creation and collapse of the air bubbles in a fluid. While they may appear to look like air, those bubbles are technically a cavity, gaseous vapor, or vacuum.

Can PD pumps run dry?

Certain Positive Displacement Pumps can run dry i.e Air Operated Diaphragm pumps have no parts requiring lubrication or no close clearances between parts. Peristaltic pumps can run dry as the hose is lubricated in a bath of its own fluid. Other types of PD pumps should not be run dry.

What happens if you run a positive displacement pump with close discharge?

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 ...

Does positive displacement pump Cavitate?

Cavitation can also occur in positive displacement pumps such as gear pumps and plunger pumps.

Why do we prime a pump?

The main objective of priming a pump is to remove the gas present. So, if the air or other gases present inside the pump casing and suction line, it must be primed before starting. But if the pump suction line and the casing are already filled with liquid during start-up, priming is not required.

Which pump must always be primed?

In short, to avoid failures, centrifugal pumps must always be primed before operating. Positive displacement pumps are self-priming with suction lift capability, but always check the operation manual or confer with an engineer to ensure the pump will properly function at start up without priming first.

Why priming is necessary before starting the pump?

Priming is the process of removing air from the pump and suction line to permit atmospheric pressure and flooding pressure to cause liquid to flow into the pump. Without priming, pumps will cease to function and break down.