Effective priming of hydraulic systems is essential for optimum performance, longevity, and damage prevention. In this article, we will explain what hydraulic pump-priming is as well as when, how, and why it is required.
What Is Pump Priming?
Pump priming is the term for removing any air from the pump itself and from the suction line. This helps the pump to work efficiently and prevents the hydraulic system from running dry causing overheating among other issues.
Benefits Of Pump Priming
Between 80 and 90% of hydraulic system issues and breakdowns are caused by contamination. Contamination is when air, water, or heat enters the system. Effective priming helps to reduce the risk of contamination keeping the hydraulic system performing better over time and can help to avoid costly repairs or replacements.
Where Priming Is Not Needed
Not all hydraulic pumps require priming. Some rely on air pressure and gravity to ensure that the suction line and pump remain air-free. Some systems are self-priming, see more about self-priming pumps below.
Are Positive Displacement Pumps Self-Priming?
Vane pumps, diaphragm pumps, lobe pumps, and internal and external rotary gear pumps all come under the umbrella of positive displacement pumps. They are all, to a certain degree self-priming.
This is because only a particular amount of liquid is moved with each rotation of the pump. They also have close-tolerance parts which act as seals, preventing air from entering the suction line. However, they must be primed manually before their first use.
Are Centrifugal Pumps Self-Priming?
Generally speaking, centrifugal pumps are not self-priming. They will either not work at all if they are started without priming beforehand, or will cause severe damage to the pump as it becomes air-bound. A centrifugal pump can be modified to make it self-priming see vacuum pump-priming and separator priming methods below.
Manual Priming pouring
Manual priming pouring involves pouring liquid into the pump to displace the air in the system.
Vacuum Pump Priming
Vacuum pump priming involves a small pump attached to the main pump that is used to pull out the air in the suction line.
Jet Pump Priming
Jet pump priming involves a jet of water being used to surround the nozzle in the suction pipe. This causes a change in pressure which pulls the air out from the sump.
This is the addition of a separation chamber and an angled piece of suction pipe to the pump to ensure that air can be released from the air vent at the top and the liquid naturally falls back down to the separation chamber.
This is where compressed air is used to create a vacuum that sucks the liquid from the sump.
Foot Valve Priming
This is the addition of a foot valve or non-return valve (NRV) at the bottom of the suction pipe that prevents liquids from escaping from the pump and suction pipe when the hydraulic pump is no longer in use.
How To Prevent Pump Operation Without Priming
In order to prevent the hydraulic system from running dry alarms (either visual or audio) can be used to alert the user to the lack of liquid in the system or shut the system down. A simple float switch works well.
Self Priming Pumps
Some pumps are self-priming, these come in three main categories:
Liquid Primed Self Priming Pumps
These are a very versatile pump as they can run with a mix of both gases and liquids. They have a priming chamber which after first use will remain full of liquid to self-prime the pump.
Compressed Air Primed Self Priming Pumps
These are able to run dry and prevent the build-up of solids. They force air into a tapered tube, creating a vacuum. This pulls out any air which is in the suction tube and the casing and releases it through the vent. An NRV then prevents any more air from entering the system.
Vacuum Primed Self Priming Pumps
These have a separate vacuum pump next to the discharge valve, usually with a float valve that pulls in liquid until it reaches the correct level.
Self-Priming Pumps Maintenance Tips
- Always prime the self-priming pump before first use.
- Ensure there are no blockages in the discharge line.
- Ensure the suction line is airtight.
- Ensure the pipes are fitted without high points which can create air pockets.
- Consider adding a strainer to remove any solids to prevent solid build up.
- Take extra care in freezing temperatures either by emptying the fluid or by keeping it warm.
- Keep your hydraulic system well maintained and serviced regularly to keep it running in peak performance.
Hydraulics Service & Maintenance
We hope that this article has helped you to understand the importance of priming your hydraulic systems, how self priming systems work and how to prime a hydraulic system to keep it serving you well for years to come.
If you need any more help in deciding which hydraulic system is best for your needs or require more information about hydraulic pumps and self-priming pumps then get in touch at MCH Hydraulics.