Analyzing Causes of Hydraulic Pump Failure
When a reliable hydraulic system suddenly starts exhibiting problems, one of the first types of components most technicians assume may need to be replaced are hydraulic pumps, yet the pump should be the last component evaluated since it is often very time-consuming to replace.
There are all sorts of “warning” symptoms a hydraulic system will exhibit long before pump failure. Some of the most common types are changes in the sounds the system makes while it is in operation. If the system suddenly starts sounding different from how it has before, this could indicate various types of problems.
Two of the more common changes in sound are a banging noise, much like water banging in plumbing pipes, and or a very high pitched shrieking noise, similar to the sound sticky car brakes make. These sounds indicate aeration and cavitation in the system, which we will discuss in more detail shortly.
Another thing to check if you notice the system is not working correctly is to verify the pump is turning. Some systems are designed so that you have to manually engage or switch the pump on. You would be surprised by how many system problems are due to the pump not being turned on!
The last thing to check before getting into troubleshooting the pump is the hydraulic fluid level. If the fluid level is too low, it will allow air into the system and cause operational problems. If you discover air in the system, you will need to remove it first to avoid pump failure.
Now that you have completed a visual and audio check of the system, you are ready to start analyzing the causes of hydraulic pump failure.
Air in the Hydraulic Pump System (Aeration)
Aeration occurs when air is introduced into the hydraulic system. This can be due to defective seals, through low tank fluid level allowing air into the pump inlet line, damaged inlet hoses and connections. It is easy to check to find out if there is air in the system as the fluid returning to tank will be foamy and the oil in the tank full of bubbles.
Operating the system when air is present may result in the pump being unable to reach the pressures required to operate the system. A by-product of this problem is the generation of excessive heat. Excessive heat is of course another reason in itself for pump failure, in this case secondary to aeration but demonstrates how the primary cause can set off a vicious circle, in this case aeration, leading to excessive heat, leading to lack of lubrication, leading to contamination issues, possible partial or full bearing seizure before complete pump failure.
Cavitation in the Hydraulic Pump System
The opposite of aeration is cavitation. Instead of air being added to the fluid, it is removed very rapidly. Cavitation is where air bubbles form quickly and collapse inward on each other within the fluid. This occurs due to a vacuum at the pump inlet as a result of an insufficient fluid supply. As in excess of 10% by volume of hydraulic fluid is dissolved air when there is an excessive vacuum at the pump inlet it is this air that is being drawn out of the oil.
The effects of cavitation can be seen around the internal pump inlet surfaces as the air is drawn out the oil it causes the removal of tiny amounts of material from the internal pump surfaces on the inlet side. This is always particularly evident in aluminum gear pumps as it leaves a slightly pock marked or frosty looking surfaces on the bearing blocks and inside of the gear housing on the inlet side.
Excessive Hydraulic Pump System Pressure
Every hydraulic pump has a maximum design pressure level. If you attempt to operate the pump at a higher pressure than it was designed for, it will cause premature pump failure. The pump simply cannot handle the excessive pressure.
Excessive pump pressure damage can include:
- Piston and barrel wear in piston pumps.
- Bent or broken vanes in vane pumps.
- Drive shaft Wear
- Excessive Gear Housing inlet side cut in track in gear pumps.
- Cracked housing
- Stripped port threads.
- Broken, Damaged and Twisted Drive Shaft
- Gear tooth breakage in gear pumps.
- Fatigue Failure
- Bearing Failure
Not to mention, the excessive pressure could also damage valves, blow seals, and hoses as it moves through the system if those parts and components are not capable of supporting the excessive level of system pressure.
Impact of Contamination on the Hydraulic Pump and System
Contaminants are one of the biggest reasons for hydraulic pump replacement. Contaminants can enter into the hydraulic system through a variety of entry points. One of the most common ones is through the hydraulic fluid reservoir.
It is easy for dust, dirt, metal shavings, and other debris to accidentally get into the fluid reservoir when fluid levels and the fluid filler are checked. Even with screens used on the suction port, small particles can still get drawn into the system. This is why it is essential to properly filter all the oil returning to the tank. It is also essential to make sure that the tank filler / breather is not damaged or blocked.
Other sources of contaminant entry include through:
- Cylinder or component wear.
- Pump wear due to cavitation, aeration, over pressure or contamination.
- Oil carbonization due to overheating.
- Fine dust being drawn in through damaged cylinder seals.
- The addition or replacement of components or sub circuits containing contaminants.
As contaminant levels grow, they can get stuck in between key surfaces such as between gear end faces and bearing block or pressure plate or between piston barrel and valve plate in a piston pump. This then leads to further wear and the generation of more contaminant and heat. The more contaminant induced wear there is to these surfaces the larger the gap becomes between these critical surfaces leading to loss of pressure capability, overheating and failure.
A buildup of contaminant particles can cut grooves into wear plates, gear teeth, and other internal parts and components. In addition, contaminants can cause blockages, which result in a buildup of excessive pressure behind the blockage leading to component blowouts.
Improper Fluid Viscosity
The viscosity of the hydraulic fluid moving through the system could lead to premature pump failure if it is not properly maintained. Having a fluid of a higher viscosity level than specified for the pump can result in cavitation within the hydraulic pump.
On the other hand, when fluid viscosity is too low, it can lead to excessive leakage between critical surfaces leading to an increase in heat generation. As such, the fluid can become too hot, overheating the entire system, and ultimately causing premature pump failure.
Extreme Heat Levels
Extreme heat is often caused as a byproduct of other hydraulic system problems. If you notice your system seems to be operating at a higher temperature than it normally does, take it as a warning sign that something is wrong. Continuing to operate the system can lead to more costly repairs.
Excessive heat levels not only cause parts and components to fail but also can damage drive shafts, housings, and other metal components. Additionally, damaged parts and components may not properly seal leading to fluid leaks. Furthermore, inside pumps, misalignment of moving parts could occur, causing internal damages that introduce contaminants into the system.
Why Hydraulic Pump Maintenance Is Essential
Many types of hydraulic pump system failures could easily be avoided with regular pump maintenance. Regular maintenance requires checking and inspecting the entire hydraulic system prior to using it. Some of the more common things you should do include:
- Check the fluid level and add fluid if needed.
- Check for signs of cracked, damaged, or broken hoses.
- Check for signs of fluid leaks around seals, connectors, valves, etc.
- Inspect the supply and return filters and change if required.
Another vital part of maintenance is replacing worn out hoses, valves, and related parts and components when they show signs they need to be replaced. It is better to replace hydraulic system parts and components before they fail. Doing so will result in low overall maintenance and repair costs. When replacing components always make certain they are clean of dust and dirt before fitting to avoid unwanted contamination entering the system.
Furthermore, hydraulic fluid should be changed periodically as it starts to slowly break down from extended use. Your objective is to ensure the fluid provides the right viscosity level required for your hydraulic operations. Always flush the system and replace the hydraulic fluid when replacing a pump or motor and be especially vigilant in removing contaminant from every nook and cranny of the system when component failure has been due to contamination damage and the source of contamination has been ascertained.
For further help troubleshooting hydraulic pump system failures, as well as all of your hydraulic system motors, pumps, parts, and component needs, please contact White House Products, Ltd. at +44 (0) 1475 742500 today!
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