Hydraulic Maintenance Info
Six routines must be followed in order to minimize the chances of your hydraulic equipment suffering costly, premature component failures and unscheduled downtime:
* Maintain fluid cleanliness;
* Maintain fluid temperature and viscosity within optimum limits;
* Maintain hydraulic system settings to manufacturers' specifications;
* Schedule component change-outs before they fail;
* Follow correct commissioning procedures; and
* Conduct failure analysis.
An effective, proactive maintenance program requires time, effort and some expense to implement. But it is cost-effective. The investment is quickly recovered through savings as a result of improved machine performance, increased component life, increased fluid life, reduced downtime and fewer repairs.
So if you own, operate or maintain hydraulic equipment, are serious about minimizing your running costs and your current maintenance practices are unsophisticated or non-existent, start implementing a proactive maintenance program today.
Contaminants of hydraulic fluid include solid particles, air, water or any other matter that impairs the function of the fluid.
How does contamination affect a hydraulic pump?
Particle contamination accelerates wear of hydraulic components. The rate at which damage occurs is dependent on the internal clearance of the components within the system, the size and quantity of particles present in the fluid, and system pressure.
Particles larger than the component's internal clearances are not necessarily dangerous. Particles the same size as the internal clearances cause damage through friction. However, the most dangerous particles in the long term are those that are smaller than the component's internal clearances.
Particles smaller than 5 microns are highly abrasive. If present in sufficient quantities, these invisible 'silt' particles cause rapid wear, destroying hydraulic pumps and other components.
How can this type of hydraulic pump failure be prevented?
While the type of failure described above is unusual in properly designed hydraulic systems that are correctly maintained, this example highlights the importance of monitoring hydraulic fluid cleanliness levels at regular intervals.
As in this case, if the high levels of silt particles present in the hydraulic fluid had been identified and the problem rectified early enough, the damage to this hydraulic pump and the significant expense of its repair could have been avoided.
What is cavitation?
Cavitation occurs when the volume of hydraulic fluid demanded by any part of a hydraulic circuit exceeds the volume of fluid being supplied.
This causes the absolute pressure in that part of the circuit to fall below the vapor pressure of the hydraulic fluid. This results in the formation of vapor bubbles within the fluid, which implode when compressed.
Cavitation causes metal erosion, which damages hydraulic components and contaminates the hydraulic fluid. In extreme cases, cavitation can result in major mechanical failure of pumps and motors.
While cavitation commonly occurs in the hydraulic pump, it can occur just about anywhere within a hydraulic circuit.
In the hydraulic valve described above, the metal erosion in the body of the valve was so severe that the valve was no longer serviceable. The valve had literally been eaten away from the inside, as a result of chronic cavitation.
In this particular case the cause of the cavitation was faulty anti-cavitation valves, which are designed to prevent this type of damage from occuring.
How can this type of failure be prevented?
This example highlights the importance of checking the operation and adjustment of circuit protection devices, including anti-cavitation and load control valves, at regular intervals.
As in this case, if the faulty anti-cavitation valves had been identified and replaced early enough, the damage to this hydraulic valve and the significant expense of its replacement could have been avoided.
Hydraulic hose failure costs and prevention
Hydraulic hose has a finite service life, which can be reduced by a number of factors. From a maintenance perspective, little or no attention is usually paid to the hoses of a hydraulic system until a failure occurs.
Hydraulic hose failures cost more than the replacement hose. Additional costs can include:
* Clean up, disposal and replacement of lost hydraulic fluid.
* Collateral damage to other components, e.g. a hose failure on a hydrostatic transmission can result in loss of charge pressure and cavitation damage to the transmission pump and/or motor.
* Possible damage caused by the ingression of contaminants.
* Machine downtime.
What causes hydraulic hose failures?
Focus on the following points to extend hydraulic hose life and minimize the costs associated with hydraulic hose failures:
External damage
Hydraulic hose manufacturers estimate that 80% of hose failures are attributable to external physical damage through pulling, kinking, crushing or abrasion of the hose. Abrasion caused by hoses rubbing against each other or surrounding surfaces is the most common type of damage.
To prevent external damage, ensure all clamps are kept secure, pay careful attention to routing whenever a replacement hose is installed and if necessary, apply inexpensive polyethylene spiral wrap to protect hydraulic hoses from abrasion.
Multi-plane bending
Bending a hydraulic hose in more than one plane results in twisting of its wire reinforcement. A twist of five degrees can reduce the service life of a high-pressure hydraulic hose by as much as 70% and a seven degree twist can result in a 90% reduction in service life.
Multi-plane bending is usually the result of poor hose-assembly selection and/or routing but can also occur as a result of inadequate or unsecure clamping where the hose is subjected to machine or actuator movement.
Operating conditions
The operating conditions that a correctly installed hydraulic hose is subjected to will ultimately determine its service life. Extremes in temperature, e.g. high daytime operating temperatures and very cold conditions when the machine is standing at night, accelerate aging of the hose's rubber tube and cover.
Frequent and extreme pressure fluctuations, e.g. rock hammer on a hydraulic excavator, accelerate hose fatigue. In applications where a two-wire braid reinforced hydraulic hose meets the nominal working pressure requirement but high dynamic pressure conditions are expected, the longer service life afforded by a spiral reinforced hydraulic hose will usually more than offset the higher initial cost.
Proactive maintenance for hydraulic cylinders
Damaged hydraulic cylinder rods and wiper seals are an eternal problem for users of hydraulic machinery. Dents and gouges on the surface of hydraulic cylinder rods reduce seal life and give dust and other contaminants an easy path into the hydraulic system. These silt-sized particles act like lapping compound, initiating a chain of wear in hydraulic components.
In response to this problem, a protective cylinder rod cover called Seal Saver has been developed and patented. Seal Saver is not a typical bellows boot you may already be familiar with. It is a continuous piece of durable material, which wraps around the cylinder and is closed with Velcro. It is then clamped onto the cylinder body and rod end. This makes installation simple with no disassembly of hydraulic cylinder components required.
Seal Saver in action
Seal Saver forms a protective shroud over the cylinder rod as it strokes and prevents buildup of contaminants around the wiper seal - a common cause of rod scoring, seal damage and contaminant ingress. Research has shown that the cost to remove contaminants is ten times the cost of exclusion. This, combined with the benefits of extended hydraulic cylinder rod and seal life, makes Seal Saver a cost-effective, proactive maintenance solution.
The top four causes of hydraulic seal failure in cylinders
Hydraulic cylinder seals cost the manufacturer pennies. They are usually purchased on a low bid basis. But that simple, inexpensive hydraulic seal can cost you thousands in downtime and loss of production if it fails. If you have a problem seal, focus on these four points to help determine the cause of failure.
No. 1 - Improper installation is a major cause of hydraulic seal failure. The important things to watch during seal installation are: (a) cleanliness, (b) protecting the seal from nicks and cuts, and (c) proper lubrication. Other problem areas are over tightening of the seal gland where there is an adjustable gland follower or folding over a seal lip during installation. Installing the seal upside down is a common occurrence, too. The solution to these problems is common sense and taking reasonable care during assembly.
No. 2 - Hydraulic system contamination is a another major factor in hydraulic seal failure. It is usually caused by external elements such as dirt, grit, mud, dust, ice and internal contamination from circulating metal chips, break-down products of fluid, hoses or other degradable system components. As most external contamination enters the system during rod retraction, the proper installation of a rod wiper/scraper is the best solution. Internal contamination can be prevented by proper filtering of system fluid. Contamination is indicated by scored rod and cylinder bore surfaces, excessive seal wear and leakage - and sometimes tiny pieces of metal imbedded in the seal.
No. 3 - Chemical breakdown of the seal material is most often the result of incorrect material selection in the first place, or a change of hydraulic system fluid. Misapplication or use of non-compatible materials can lead to chemical attack by fluid additives, hydrolysis and oxidation reduction of seal elements. Chemical breakdown can result in loss of seal lip interface, softening of seal durometer, excessive swelling or shrinkage. Discoloration of hydraulic seals can also be an indicator of chemical attack.
No. 4 - Heat degradation is to be suspected when the failed seal exhibits a hard, brittle appearance and/or shows a breaking away of parts of the seal lip or body. Heat degradation results in loss of sealing lip effectiveness through excessive compression set and/or loss of seal material. Causes of this condition may be use of incorrect seal material, high dynamic friction, excessive lip loading, no heel clearance and proximity to outside heat source. Correction of heat degradation problems may involve reducing seal lip interference, increasing lubrication or a change of the seal material. In borderline situations consider all upper temperature limits to be increased by 50 degrees F in hydraulic cylinder seals at the seal interface due to running friction caused by the sliding action of the lips.
Here's a secret - it is not necessary to buy replacement seals from the hydraulic cylinder manufacturer. Many hydraulic seal suppliers have the same exact seals that are used in most hydraulic cylinders and can easily cross reference or match up a replacement. In many cases, if there is a recurring problem with a seal, your seal specialist can recommend a solution and increase the life of the seal.
Adding hydraulic oil - without the dirt
Hydraulic fluid straight from the drum, has a typical cleanliness level of ISO 4406 21/18.
A 25 GPM pump operating continuously in hydraulic oil at this cleanliness level will circulate 3,500 pounds of dirt to the hydraulic system's components each year!
To add hydraulic oil, and not the dirt, always filter new oil prior to use in a hydraulic system.
This can be accomplished by pumping the oil into the hydraulic reservoir through the system's return filter. The easiest way to do this is to install a tee in the return line and attach a quick-connector to the branch of this tee. Attach the other half of the quick-connector to the discharge hose of a drum pump.
When hydraulic oil needs to be added to the reservoir, the drum pump is coupled to the return line and the oil is pumped into the reservoir through the return filter. As well as filtering the oil, spills are avoided and the ingress of external contamination is prevented.
The benefits of carrying out this simple modification are well worth the minor cost involved.