At Royal, we work with our customers to review their failures and use that information to provide a solution.
You can use the list below to diagnose what type of failure your cylinder is up against and possible solutions. Or send your cylinder to us and our engineering team will review the cylinder and go over the application with you to develop a custom cylinder solution.
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|PISTON ROD||Scored or Scratched||
|Bent or Broken||
|Worn on one side or spot||
TROUBLE SHOOTING HYDRAULIC CYLINDERS
4 locations and 10 spots to check if your hydraulic cylinder is leaking! Find the reason for the leak.
and Heads Between Gland
Bushing and Rod
Bushing and Heads
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Inspection and Repair of Royal Hydraulic Cylinders.
This bulletin is to assist field service people in the inspection and rebuilding of Royal Hydraulic Cylinders. Most of the general techniques are also appropriate for servicing air cylinders.
1. Observation of Cylinder in Operation.
If possible, it is very useful to observe the cylinder in operation prior to removal. Look for these signs of application problems.
- - Unusual lateral movement during extension/retraction will indicate side load.
- - Slow sideways swaying during extension will indicate misalignment.
- - Check for binding of the mounts at the extend/retract positions. Check also for heads/tie rods hitting machinery frames.
- - Look for proper hose clearance; make sure the hoses have sufficient slack for all positions of the cylinder.
- - Mark the rod to indicate the orientation of the rod to the head and gland bushing while it is still connected to the machine.
- - Look for leak source i.e. leakage from rod vs. leakage between gland and head, a barrel seal leak or weeping port.
- - Broken trunnion mounts or pins are a clear sign that the cylinder is not aligned to the load.
2. Outside Inspection after Removal from Operation Prior to Disassembly.
- - Mark head barrel and gland bushing to indicate relative position before disassembly. This is critical in determining alignment of wear patterns between the piston, barrel, rod and gland.
- - Check for binding on trunnion pins. This will show up as galling or a smeared pin surface cause by insufficient lubrication. This can be polished out if it is minor but for any major wear, the trunnion must be replaced. Polishing them until they are undersized will cause lost motion in the mounting and impact wear on the pins and their bushings.
- - Extend rod to full stroke and look for obvious rough spots. Rod damage near the clevis end caused from channel locks or vice grips is a common cause of seal failure.
- - Look for long parallel scratches on the rod and if present, mark bushing to indicate location.
- - Look for oval wear patterns at the ends of stroke. This will indicate binding of the rod at stoke ends.
- - Look for pitting of the rod if chrome plated. Chrome will fail due to undersurface corrosion starting at the clevis threads.
- - Check heads and tail mounts for signs of physical contact Tail lugs in a bind will have grooves on the inside faces. Check rod ends clevis as well for similar wear indicators.
- - Check mounting holes for elongation.
- - On rare occasions, severe pitting can show up randomly on the rod. Look for a similar reversed pattern on the inside of the gland. If present, this is an indication arcing. This will occur if the cylinder has somehow been in the a ground loop of a welding operation. The welding current passing through cylinder will cause arcing where internal surfaces are in contact. If this has happened, the rod must be scrapped as the pitting will cause rapid gland seal failure.
3. Oil Sample.
- - Take a fresh oil sample from inside the cylinder being careful not to contaminate the sample with exterior dirt.
- - Check oil color. Overheated oil has burnt smell and dark color. In this condition, the oil has lost most of the additives (such as wear reducers and viscosity stabilizers) and is starting to break down through oxidation. Burnt oil can be caused by incorrect relief valve setting ( i.e. set below system pressure so that the relief is by-passing all the time) or from failed/plugged air or water coolers.
- - Put some oil sample on white paper and look for metal particles. Cylinders will collect metal particles in seals and grooves that deposit from contaminated oil.
- - A leaking cylinder with a worn rod wiper/scraper will cause oil contamination. The wet rod will attract debris that will be pulled back into the cylinder upon retraction.
- - Metal particles or filings indicate metal to metal contact in the system. Steel particles (silver color) can be from pump, valve or cushion sleeve failure. The presence of steel can be tested by using a magnet to collect the wear particles. Brass/Bronze particles are a usually a result of bushing wear.
- - Stroke the cylinder manually in both directions to purge oil from inside. Fully retract the rod into barrel.
- - Remove front plate and check the bushing fit in the head and plate. Check that the bushing is held tightly in the head by the plate. A loose bushing will cause wear in the head and bushing due to fretting. Fretting is the wear caused by very small rapid movement of one part against another.
- - Remove gland end head from barrel and separate from rod.
- - Remove bushing from head.
- - Remove barrel, tie rods and blind end head.
- - Remove piston from rod if worn or loose.
5. Inspection of Internal Components
i. Piston/Piston Rod
- - Check piston for signs of contact with barrel. This will happen if the barrel is out of round or the wear strip on the piston is worn. Extreme gland bushing wear can also cause piston/barrel contact at full extend.
- - Check clevis thread. If this is bent or cracked, the clevis is binding on the machinery and will cause severe rod and bushing side load. Look for pounded out metal at the clevis root.
- - Check piston seals for signs of bypassing. This would be seen as a smooth rippling along the sealing edge. A torn out look to the lip edge indicates cavitation from an over-running or negative load.
- - Check cushion sleeves for signs of contact with heads. Sleeves will contact head at full extension when the gland bushing is severely worn and/or side load is present. Blind end sleeve wear indicates the heads are out of square to the barrel or the piston nut is worn or not square to the piston.
- - Remove piston seal and check for metal particles or filing in the groove bottom. They will collect over time if the oil is contaminated
- - If the cylinder has been subjected to overheated oil, the seals will be brittle. The normally blue or orange color will be dark brown. O rings will be stiff and deformed.
- - If the piston was loose on the rod at the time of disassembly, , it may have deformation where the piston nut secured to the rod. If deformation is present, the piston should be scrapped. This is because the uneven surface under the piston nut will cause the nut thread to bend as it is tightened. This will cause the cushion sleeve to bend off the rod centerline.
ii. Gland Bushing Wear
Check for excessive gland bushing wear. This can be caused by:
- - Contaminated oil. Leaking cylinders will contaminate an oil system if the rod scraper allows debris into the cylinder upon retraction
- - Failure of the rod wiper. This will cause outside contamination to be drawn into the gland and past the bushing, causing rapid wear of both elements.
- - Side Load. Cylinders are structural elements only for loads applied along their axis. They are not meant to resist side load and will fail quickly under side load unless specifically designed for that purpose. Check the wear pattern on the bushing and compare it to the rod and tail mount. Often a side loaded bushing failure is matched by tail hold wear marks.
- - Incorrect bushing installation in head. Although normally not a common problem, if the bushing is not square in the head when front plate is assembled, the bushing may bind on the rod. This would happen if there were debris under the bushing lip during assembly.
- - Rod damage. Tools contacting the rod surface anywhere along the stroke can cause damage. This is common at the clevis end where the rod has been screwed into the clevis with improper tools. Any jaw mark or gouge will tear a seal immediately and cause leaks and wiper failure. This then allows more debris into the cylinder causing oil contamination and bushing wear.
- - Paint. Check for over-spray on the rod if the area was recently painted. This can happen on new and rebuilt equipment or from sloppy painting nearby. The rod scraper will not remove paint and will cause seal/scraper failure.
- - Excessive line length. On rare occasions, contamination will build up in the cylinder because the line volume between the cylinder and the valve exceeds the cylinder displaced volume. This causes the same volume of oil to shuttle back and forth between the valve and the cylinder, but never get through the valve to be returned to tank for filtering.
iii. Gland Bushing Inspection
- - Check spiral oil groove as a wear indicator. Severe wear will show as a high polish on one side will obvious out of round to the bore. Bushings with excess of .010” radial wear should be scraped. Excessive bushing wear causes local seal compression and deformation, feathering of the seal lip and heal leading to blow out. Bushing wear also causes the cushion to enter the gland end head off center, which will cause metal to metal contact. This will introduce metal particles into the system.
- - Check for a rippled edge to the seal. This indicates the seal is leaking at a point on the edge, which causes rapid erosion of the lip edge.
- - A torn seal indicates a rough spot on the rod or improper assembly during the last rebuild.
- - Seal components should be pliable and near to original color.
- - Check barrel for axial grooves caused by piston scraping.
- - Barrels usually have a long life if the cylinders are free of foreign particles.
- - Minor scratches up to .010” deep can be honed out by a qualified honing shop.
- - Dented or exterior worn barrels must be scrapped. Even if the dent can be straightened out, it is now a potential failure point under pressure. A barrel with wear on the outside will eventually fail due to metal fatigue in the roots of the scratches.
- - Check heads for port damage and damaged retaining plates.
- - Check heads for internal face damage. This would indicate the piston is slamming into the head due to poor cushioning or excessive load.
- - Check for oversize or elongated mounting holes.
- - Seals should be replaced if there is any doubt about their condition. This is one of the least expensive spares to change in the cylinder If the cylinder has been in continuous service over 3 months, the seals should always be changed.
- - NEVER, NEVER, NEVER use WD40 or similar volatile solvent (CRC) on urethane seals during re-assembly. Urethane absorbs WD40 and will cause swelling and rapid failure if used.
- - ALWAYS use clean hydraulic oil to ease seals into place during assembly.
- - Use blunt tools that will not scratch or tear seals. A slotted screwdriver can ruin a piston or gland seal. Modified plastic paint brush handles work well for easing seals into place.
- - Check piston for wear on o.d. and seal grooves. Seals can slowly wear grooves out of shape to the point that proper sealing is no longer possible. The piston faces where the nut and rod seats should also be flat and true. Unevenness here will cause nut and rod failure.
- - Always Use Factory Tie rods and New Tie Rod nuts. Factory tie rods are made of high strength steel that are made to be tensioned without deformation. Use of other materials poses a risk of tie rod failure, machine damage and personal injury.
- - DO NOT RE USE OLD TIE ROD NUTS. These nuts as supplied from the factory are single use nuts that have a built in nylon locking ring. The locking performance of these nuts are greatly reduced when used a second time as nylon has already been deformed.
A CLEAN WORK AREA IS CRITICAL TO SUCCESSFUL CYLINDER REBUILDS
- - Replace all seals for the piston, gland, and heads.
- - If the clevis threads are of smaller o.d. than the rod, then the piston can go onto the rod directly.
- - If the clevis threads are full diameter, then the gland bushing (already fitted into the head) must be installed from THE PISTON END OF THE ROD so as not to cut the gland bushing rod seals on the rod end threads.
- - Fit piston nut to rod and torque to the value listed in the attached table. Proper torque of the piston nut is essential to ensure the piston does not loosen in service.
- - Stand barrel vertically on a bench without heads.
- - Lubricate the piston and barrel top edge. Slide the piston/rod assembly into the top of the barrel in a rocking motion. This will ease the seals past the lip of the barrel.
- - Watch out for seal lip folding as the last of the seal passes the lip. Use a blunt tool (plastic or brass) to push the lip past the barrel edge.
- - Slide on the gland end head with gland bushing pre-fitted.
- - Lay assembly horizontal on bench and fit blind end head.
- - Align ports, fit front plate and install tie rods. Be sure rod is fully retracted into the cylinder before tie rods are tightened. This reduces the tendency to pull the heads off-square with the barrel.
- - Tighten tie rods in criss-cross pattern to ensure the heads are pulled straight onto the barrel ends.
- - See attached table for tie rod torque specifications.
- - Pressure test for leaks and binding of rod.
- - Fit ports with plastic port plugs when finished.
7. SET UP OF ASSEMBLED CYLINDERS
i. Needle Valve Setting
- - Adjust the needle valve to sufficient enough to eliminate hard contact of the piston to the heads.
- - Excessive cushioning caused extreme pressures to build up in the cylinder that add extra strain on the seals.
- - A good starting point for the needle valve position is screw the needle valve all the way in until it is hand snug. then back off ½ to 5/8 of a turn.
ii. Remounting on machinery
- - Check mounting brackets on machinery for wear and cracks. Worn pins and mounts create slop that applies shock loads to the cylinder during operation. Shock loads from worn parts are 2 to 3 times as large as the normal cylinder forces. This repeated pounding also eventually causes metal failure in the machine frame, broken welds and spider cracks forming in the frames.
- - Re check cylinder alignment. Even moderate misalignment will cause rapid wear of new gland bushings and seals.
- - Trunnion mounted cylinders have zero lateral flexibility and therefore must be aligned very carefully. Both extension and retraction positions should be checked. If the connected load pivot is not parallel to the trunnion centerline, the cylinder will be pushed side to side through its stroke. This will rapidly break the trunnion mounts or pins.
- - Cylinders under no circumstance can be used as machine guide mechanisms. All external guide loads must be taken by the machine mechanism. All loads seen by the cylinder must axial to the cylinder. The cylinder cannot withstand side loads or bending moments applied to rod end or cylinder body.
- - Check that the rod clevis does not bind at full extension or retraction.
- - Always keep ports plugs in place until hose connections are made.
Royal Cylinders are designed to be mill-serviced for many years of operation. Re-using worn parts is false economy which will lead to shortened life and poor performance. Any spare part can be obtained for replacement. A full rebuild of a Royal cylinder should return the cylinder to factory standards.
Brian Rooney, P.Eng.,
December 9, 2015
Bulk Service Bulletin
Topic. – Cylinder Storage.
- 1. Do not store cylinders outside for any length of time. Exposed surfaces including the chrome rods can rust quickly and will cause rapid failure of seals and bushings.
- 2. Do not spray rods or cylinders with CRC, WD40 or other water displacement chemicals. Theses chemicals cause the urethane seals to swell thus leading to premature seal failure or cylinder jamming. Use a proper soluble wax rust preventer if required. A light mineral oil can be used to coat the inside for cylinders that will be stored longer than 6 months.
- 3. Do not dismantle cylinders in stores to salvage spare parts. The spare cylinder at this point is useless although it may appear to be intact and functional. Tie rod tension may be in correct which may result in cylinder failure of persona injury in the event of a tie rod failure or cylinder leak.