Cylinders are almost as numerous as pumps and motors together as a product group. Because they are less intricate than other types of hydraulic components, they are generally simple to fix. As a result, many hydraulic equipment owners do their own cylinder repairs.
The following is a guide to performing effective hydraulic cylinder repairs. The extent of the repair work that can be done in-house is determined by the extent of wear or damage to the cylinder and the size of your repair shop. The economics of repairing a cylinder, like any other repair, are ultimately determined by the cost and availability of a new one.
Inspection and disassembly
A cylinder is typically removed for repair owing to either exterior or interior leaks. After disassembly, a close study of the cylinder parts, particularly the seals, can identify faults that would otherwise go undetected.
Piston Sealing
The barrel is large or has bulged in service if the piston seal is significantly deformed, corroded, or missing. The barrel or the entire cylinder should be replaced in this scenario. Replacing the piston seal without replacing the barrel is a temporary fix that will necessitate comprehensive maintenance at the earliest opportunity.
Rod
Using a dye penetrant, inspect the rod for cracks at any spots where its cross-section varies. Examine the rod's chrome surface. The rod is bent if the chrome appears dull on one side and polished on the other. When repairing a cylinder, rod straightness should be examined. This is accomplished by rolling the rod and measuring the run-out using a dial gauge (Figure 1). Position the rod so that the distance between the rollers (L) is as large as possible and measure the run-out at the midpoint between the rollers (L/2).
Bending rods may usually be straightened in a press. Straightening rods without destroying the hard-chrome plating is occasionally achievable; however, if the chrome is destroyed, the rod must be rechromed or replaced.
The efficiency and service life of rod seals are diminished when the chrome surface of the rod is pitted or scored. Minor scratches in the chrome surface can be polished out with a crosshatch motion using a strip of fine emery paper. If the chrome has become severely pitted or scored, the rod must be rechromed or replaced. For small-diameter rods, machining a new rod from hard-chrome plated round bar is usually the most cost-effective solution.
Rod Sealing
When the rod seal is badly warped, the guide bush is frequently overly worn or the rod is bent. In both circumstances, the weight of the rod rides on the seal, causing it to fail. Replacing the rod seal without recognising and correcting the underlying cause is a band-aid solution.
Head
In light-duty cylinders, the rod is commonly supported directly on the head material, which is usually aluminium alloy or cast iron. In applications where the rod is subjected to high loads, a metallic or nonmetallic guide bush (wear band) is installed between the rod and the head. A bush between the rod and the head on a cylinder should be replaced as part of the repair.
If the rod is supported directly on the head, measure the internal diameter of the head with an internal micrometre or vernier calliper. To check for ovalness, take measurements in two spots, 90 degrees apart. The head's internal diameter shall not be greater than the nominal rod diameter plus 0.004 inch. If the nominal diameter of the rod is 1.5 inches, the internal diameter of the head shall not be greater than 1.504 inches. If the head measures outside of this tolerance, the rod will be able to load the rod seal, resulting in premature seal failure. As a result, the head must be sleeved with a bronze bush or replaced with a new head made of a similar material.
Minor scoring on the lands of the seal grooves inside the head has no effect on cylinder function as long as the maximum diameter across the lands does not exceed the nominal rod diameter + 0.016 inch. If the nominal diameter of the rod is 1.5 inches, the inside diameter of the head, measured across the lands of the seal grooves, should not be greater than 1.516 inches. If the seal lands exceed this tolerance, the rod seal's service life will be reduced. As a result, the head must be replaced with a new one made of a similar material.
Barrel
Check the barrel for internal pitting or scoring. The efficacy and service life of the piston seal are compromised if the barrel is pitted or scored. As a result, the barrel must be sharpened or replaced to remove the damage. Pitting or scoring less than 0.005 inch deep on small diameter barrels can be eliminated with an engine-cylinder honing tool. The barrel must be sharpened uniformly all the way down its length.
For standard-size piston seals, the maximum bore diameter is the nominal bore diameter plus 0.010 inch. For example, if the barrel's nominal bore diameter is 2.5 inches, the maximum size after honing should not exceed 2.510 inches. Using an internal micrometre, this size should be examined at many spots along the barrel.
If scoring or pitting remains at 0.010 inch oversize, the barrel must be honed further or replaced to accommodate oversize seals. For small-diameter cylinders, making a new barrel from sharpened tubing is usually the most cost-effective option.
Large diameter, inch-size cylinder barrels can be salvaged by honing them 0.030 inch or 0.060 inch oversize and fitting the appropriate oversize piston seals. Because oversize seals for metric-size cylinders are in short supply, it is not always possible to salvage metric-size barrels by fitting oversize seals.
Piston
In light-duty applications, cylinder pistons are typically machined from aluminium alloy or cast iron and function in direct contact with the cylinder bore. Minor scoring on the outside diameter of the piston has no effect on cylinder function as long as the minimum diameter of the piston is more than the nominal bore diameter minus 0.006 inch. An external micrometre can be used to verify this. If the nominal diameter of the barrel is 2.5 inches, the minimum piston diameter is 2.494 inches. If the piston diameter exceeds this tolerance, it must be replaced with a new piston machined from a comparable material.
In cases where the rod is subjected to high loads, nonmetallic wear bands are installed between the piston and barrel. If the cylinder has piston wear bands, they must be replaced as part of the repair.
Purchasing Seals
Avoid the frequent practise of measuring the old seals when obtaining seals from a seal supplier. In service, seals can shrink or swell, and an improper seal may have been fitted previously. To ensure that you receive the correct seals, use a vernier calliper to measure all seal grooves and provide this information to your seal supplier.
Assembly
Clean all parts thoroughly with a petroleum-based solvent and blow-dry with compressed air. During assembly, coat all parts with clean hydraulic fluid. Check that the seal grooves are clean and free of nicks and burrs before installing the seals. When installing seals, avoid using a screwdriver or other sharp object, as this can damage the seal. After assembling the cylinder, plug the service ports to prevent moisture or dirt from entering.
https://www.hydrostaticpumprepair.com/
We know what it takes to complete everything from simple, quick cylinder repairs to comprehensive projects with maintenance downtimes. We employ world-class simulation tools, extensive 3D drawing capabilities, and finite element analysis skills to determine failure modes, anticipate future failures, and recommend general product changes for optimum performance and dependability. Decades of application experience combined with cutting-edge instruments means better recommendations and, eventually, better cylinder repairs.
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