Article content

1. What is pump priming?
2. When is priming performed on a pump?
3. Méall of Priming
4. Conclusions

Introduction

Priming is an operation prior to the moment when the pumps are put into operation and it is also one of the procedures in which the people in charge of the care and operation of these instruments fail the most.

What is pump priming?

It is a process that is applied to the suction chamber and casing lines with the same liquid that will be pumped. One of the main objectives of this procedure is to ensure the correct operation of the pump. Regarding the role played by the liquid used for priming, it could be said that it replaces the air, gas or vapor that may be found in the pump lines.

When is priming performed on a pump?

Performing a priming process on a pump can occur in two cases:

When you have a positive suction charge

A positive suction head means that the level of the liquid to be pumped is higher than the pump shaft itself. When this happens, it is necessary to expel the air in the piping and pump casing when the pump is put into operation. This also involves valves and bleed plugs.

Priming process in case of positive suction load:

• All suction valves are opened to allow liquid to enter the suction pipe and pump casing.
• The air relief valve, usually located at the top of the casing, opens.
• The pump is fully primed when the liquid starts to flow continuously, i.e. without air bubbles.

Priming process when there is a negative suction charge:

• When these conditions occur, it is recommended to use a By Pass or side weight on the discharge check valve, which would allow the use of the liquid in the same release line.
• Use a suction valve, similar to a foot valve. This type of valve (foot) will help retain the liquid present in the suction pipe and pump casing once the pump has been initially primed.

Méall of Priming

What methods can we apply to prime a pump?

We can apply different methods when priming a pump, which may vary according to the needs and operating fundamentals.

By gravity

This method could be considered as the simplest way to prime a pump and the way to do it would be to install the pump in such a way that air pressure and gravity do the job.

How is this done? A relief valve is installed at the top of the casing and opens when the pump is started to ensure that all air is removed.

A very convenient thing to keep in mind with this priming method is the installation of a switch on the suction tank, which would help to stop the pump in case the liquid descends below the suction pipe.

With a vacuum pump

This type of method is generally used to prime medium to large pumps and avoids the use of the foot valve.

Another advantage of this priming method is that a single vacuum pump can be used to carry out the same process in several units and only the necessary air connection is required to all pumps.

The exercise performed in this priming method causes a vacuum to be created at the top of the casing, allowing the air to be removed and the fluid to move to the top of the casing.

The vacuum system will remain closed, therefore it will be necessary to install a sight glass tube or other liquid level indicator above the pump, so that the technician will be able to observe when the system is filled. Once this is completed, the vacuum operation should be performed.

Something to keep in mind once the priming process is finished with this method is the isolation of the suction tank in order to avoid recirculation and low pump performance.

With ejector or aspirator

The priming process in a pump operating below a suction lift can be performed through an ejector or aspirator installed above the pump casing.

In this method, compressed air, steam and water sent through the aspirator or ejector reduce the pressure at the top and allow the fluid to rise and exit through the relief valve.

One thing to keep in mind in this priming method is to open the valve on the discharge pipe near the pump and open the suction pipe and then connect the ejector. When the ejector starts, the continuous discharge of the fluid will begin. At this point the pump should be turned on.

Manual

Priming a pump in manual method, consists of operating a foot valve, also known as a check valve and usually installed at the base of the suction pipe.

Also, it is necessary to close the gate valve on the discharge and then add liquid to the top of the pump casing until the liquid spills out.

This method works because the check valve allows the fluid to circulate in only one direction in the suction pipe. This process allows the liquid column not to flow backwards in case of equipment stoppage, keeping the installation primed.

One thing to keep in mind with this method is frequent inspection and cleaning of the foot valve. Although this method is simple and inexpensive, it is recommended only for pumps with low flow rates and should be used only when there is no other way to prime.

Conclusions

• Priming is an operation prior to the moment when the pumps are put into operation.

• One of the main objectives of priming is to ensure proper pump operation.

• Performing a priming process on a pump can occur in two cases.

• We can find 4 priming methods