Hydraulic RAM Overhaul and Repair

Hydraulic RAM Repairs UK Ltd offer comprehensive Hydraulic RAM repair and service.

Following arrival at our Mitcham workshops, we closely examine all parts of the cylinder after disassembly, especially the hydraulic seals, as this may reveal problems that may not otherwise be apparent.

Piston seal - If the piston seal is badly distorted, eroded or missing completely, this normally indicates that the barrel is oversize or has bulged in service. In this case, we recommend the barrel or the complete cylinder should be replaced. Replacing the piston seal without replacing the barrel is false economy, and in the longer term, may lead to further breakdown in the future. Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

Rod seal – On inspection, if the rod seal is badly degraded or distorted, this usually indicates that either the guide bush is excessively worn or the rod is bent.  Regardless, this results in the weight of the rod riding on the seal, which causes it to fail. Replacing the rod seal without identifying and rectifying the cause of the problem is a short-term fix only.Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

Piston Rod – We check the rod for cracks at all points where its cross-section changes. Penetrant Dye may be helpful in this regard.  It is simple to use and readily available from industrial hardware outlets.

We carefully inspect the chrome surface of the rod. If the chrome looks dull on one side and polished on the opposite side, this indicates that the rod is bent. Rod straightness should always be checked when a cylinder is being repaired. This is done by placing the rod on rollers and measuring the run-out with a dial gauge.
In most cases, bent rods can be straightened in a press. It is sometimes possible to straighten rods without damaging the hard-chrome plating, however if the chrome is damaged, the rod must be either re-chromed or replaced.

If the chrome surface of the rod is pitted or scored, the effectiveness and service life of the rod seals will be reduced. Minor scratches in the chrome surface can be polished out using a strip of very fine emery paper. However, if we find the chrome is badly pitted or scored, the rod must be either re-chromed or replaced. Machining a new rod from hard-chrome plated round bar, which is available in standard sizes from specialist steel suppliers, is usually the most economical solution for small diameter rods.

Before a rod can be re-chromed, the existing chrome plating has to be ground off. Each time a rod is ground, the diameter of the parent metal is reduced and therefore the thickness of the chrome layer required to finish the rod to its specified diameter increases.Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

Head – It is usual, in cylinders used in light-duty applications, for the rod to be supported directly on the head material, which is typically aluminium alloy or cast iron. A metallic or non-metallic guide bush (wear band) is fitted between the rod and the head where there are high loads on the rod. If a cylinder is fitted with a bush between the rod and the head, it should be replaced as a matter of routine as part of the repair.

If the rod is supported directly on the head, we use an internal micrometer or vernier calliper to measure the head’s internal diameter. We take measurements in two positions, 90 degrees apart, to check for ovalness. The inside diameter of the head should not exceed the nominal rod diameter.

Minor scoring on the lands of the seal grooves inside the head is not necessarily harmful to the function of the cylinder, as long as the maximum diameter across the lands does not exceed the nominal rod diameter.  If the seal lands measure outside the accepted tolerance, the service life of the rod seal will be reduced. Therefore, we recommend the head is replaced with a new head, machined from a similar material. Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

Barrel – We inspect the barrel for internal pitting or scoring. If the barrel is pitted or badly scored, the effectiveness and service life of the piston seal will be reduced. If so, we recommend the barrel is honed to remove damage or be replaced. On small diameter barrels, pitting or scoring less than 0.005” deep can be removed using an engine-cylinder honing tool or similar. The barrel must be honed evenly along its full length.

Manufacturing a new barrel from honed tubing, which is available in standard sizes from specialist steel suppliers, is usually the most economical solution for small diameter cylinders. Large diameter, inch-size cylinder barrels can be salvaged by honing either 0.030” or 0.060” oversize and fitting the corresponding oversize piston seals. In our experience, oversize seals for metric-size cylinders have limited availability and therefore it is not always possible to salvage metric-size barrels by fitting oversize seals. Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

Hydraulic Piston – The pistons of cylinders used in light-duty applications are usually machined from aluminium alloy or cast iron and operate in direct contact with the cylinder bore. Minor scoring on the outside diameter of the piston is not detrimental to the function of the cylinder, as long as the minimum diameter of the piston is not less than the nominal bore diameter minus 0.006”. This can be checked using an external micrometer.  If the piston diameter measures outside the accepted tolerance, we recommend it is replaced with a new piston, machined from a similar material.

Non-metallic wear bands are fitted between the piston and barrel, in applications where there are high loads on the rod.  If the cylinder is fitted with piston wear bands, these should be replaced as part of the repair. Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

Replacement Seals - To ensure we fit the correct seals, we measure all seal grooves with a vernier calliper and provide you with information on the seal manufacturer. Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

Assembly - We carefully clean all parts in a petroleum-based solvent and blow-dry using compressed air. Coat all parts with clean hydraulic fluid during assembly. Prior to installing seals, we ensure that the seal grooves are clean and free from nicks and burrs.  Special care is taken by us when we install seals, as this can result in damage to the seal. After the cylinder has been assembled, we plug its service ports to prevent ingress of moisture or dirt.   All the above work is carried out in a special ‘clean room’ at our Mitcham workshops. Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

For further information on Hydraulic RAM Overhaul services we offer please contact our Mitcham offices.