It is never a good day when you suspect that there is something “not quite right” with your hydraulic pump. You might notice an unfamiliar noise or that things are running hotter than usual or operating slower than usual. Your ears and your eyes — and even your intuition about something being abnormal — these are your first line of defense to prevent hydraulic pump failures.

Since contamination is a major reason for pump failures it is important to have a basic understanding of the four general categories of contamination that most often affect hydraulic pumps.

These include built-in contamination, ingressed contamination, water/moisture contamination, and internally/externally generated contamination.

The following is a synopsis of material from a webinar hosted by Paul Heney, vice president and editorial director for Fluid Power World and presented by Josh Harrison, a technical customer service representative for FluiDyne Fluid Power, in December 2018. The transcript of this entire webinar can be found at

Built-in contamination refers to contamination that occurs during the hydraulic pump manufacturing process.

This type of contamination can be caused by burrs and chips that remain behind from the machining of parts. Dirt and cloth fibers from the wiping of parts can also be left behind. This type of contaminant will usually flush through the pumps and filters once the system is operational and may leave behind some wear and scoring, but usually this built-in contamination doesn’t do any noticeable internal damage.

Ingressed contamination occurs when dirt, debris, water or other contaminants enter the system from the outside.

Ingressed contaminants can be introduced into the system through new oil that is already contaminated, through dirt, dust and water that infiltrate seals or reservoirs with inadequate breathers, when a line is disconnected and left dangling near a debris-laden floor or the system is opened up for any reason, including routine maintenance. The debris that collect on worn seals on cylinders and pumps will eventually wear on them, causing pieces to eventually move through the system, scoring cylinder rods and motors and internal parts on the pump.

Breather quality is also an important contributor to ingressed contamination.

If the breather is plugged or is not of high quality, it will pull in dirt, soot and ash from the system. Combine that debris that is sucked in with a low level of oil inside the tank and that debris will eventually settle in the bottom on the tank and start infiltrating the system. Changing or cleaning out the breather can prevent ingressed contamination issues.

Water/moisture contamination is not the most common source of contamination, but it does occur.

Humid environments can cause moisture build-up which can affect viscosity of oil. Older breathers can pull in surrounding atmosphere. If moisture is present, the breather will suck it in so it is important to inspect breathers regularly. Pressure washing machinery that has old or damaged seals can cause moisture issues. Mixing two different types of oil can also affect viscosity, which can damage hydraulic pump components and seals. If the oil is contaminated with moisture it will appear milky and white and may have sludge build up.

The most common type of contamination is internally and externally generated. This category of contamination generally has four major causes – cavitation, aeration, abrasion and parts failure.

Cavitation is a restriction on your inlet created by a pump which is trying to pull in more oil than what your line is able to supply, creating an inlet vacuum. Vapor bubbles in the inlet vacuum explode and pit your plates, the bottom of your cylinder block and other parts and your piston heads start to get sloppy. If you see any depth of pitting, the cavitation or aeration process is present. This is especially prevalent when a pump is replaced. The new pump, running more efficiently than the old pump, tries to pull more oil in and the system is not able to keep up with the demand. Rather quickly the new pump will fail if everything is not cleaned out.

Aeration is similar to cavitation but is caused by air in the system. Cam rings affected by aeration display wash-boarding and a lot of ripples. Piston heads start to get rounded and start to smear. Aeration will cause vein and piston pumps to be damaged fairly quickly. Greasing around all connections, especially the inlet connections, can verify that you are not pulling in any air through those connections.

Abrasion is caused by all the debris that are not caught in the filtration system. Even the smallest grains of sand can wear parts down and reduce efficiency over time. With abrasion you will see grooves and scoring. Gear and vane pumps can usually pass larger particles, but piston pumps can be problematic because of the tight tolerances between the system and bore. Even with a good filtration system on the outlet of your pump, a tank is still going to contain a lot of contaminants that can pass through your pump. Cleaning the tank is especially important when putting replacement pumps into service.

Parts failure is another common cause of internally and externally generated contamination. Generally a parts failure is obvious. Unfortunately by the time your pump has completely failed a lot of the pieces which broke off have moved through the system, plugging up filters and often damaging valves and cylinders. You will need to invest a lot time repairing the damage and cleaning and changing oil and filters. Parts failure can often be avoided through routine maintenance and inspections.

Servo Kinetics is a full-service hydraulic repair, inspection and rebuild facility that delivers the highest quality standards at the lowest possible cost. If you need help with industrial hydraulic repair services including Vickers classic factory rebuilds and EHC energy pump repair, or are looking for reverse engineering services, or new pumps and motors, we can help. Call us to learn more about our services, and ask about our Special Offers!