Hydraulic Cylinder Assembly
Get An Instant QuoteSeal Fitting and Cylinder Assembly Steps
Proper installation of seals is essential to prevent internal and external leakage of the hydraulic cylinder. The procedure begins with pre-fitting seals on the piston and guide sleeve, then assembles the piston rod, cylinder tube and cylinder head, and installs oil port fittings and protective covers in the final step.
1.Pre-Assembly
The first step for seal installation and full cylinder assembly is component pre-assembly. That means we fit sealing rings, wear rings and back-up rings onto the piston. Meanwhile, we install seals and dust rings on the guide sleeve. First, we check the part number, material, batch number and shelf life of the sealing components such as sealing rings, back-up rings and dust rings, and we never mix them up or swap seals without approval. Next, we carefully check the seals to confirm the lip direction and make sure it is correct for later assembly. The lip of the piston’s main seal faces the hydraulic oil side. This keeps working pressure inside the cylinder and stops internal leakage. For the guide sleeve, its main seal lip faces the cylinder’s inner oil chamber. This way, oil pressure presses the sealing lip tight and stops hydraulic oil leaking out along the piston rod. And the dust ring lip faces the outside of the cylinder to keep dust, mud and water out of the cylinder.We also check seal surfaces for scratches, burrs or aging marks to make sure there are none, then coat them with matching grease before assembly, so the seals will fit in easily.
When we fit the seals, we use a tapered installation sleeve to fit sealing rings, wear rings and back-up rings onto the piston, and use a nylon press sleeve to push the guide sleeve’s main seal and dust ring evenly into the grooves. We never pry seals with screwdrivers, needle-nose pliers or other sharp tools, because sharp edges can nick the sealing lip while fitting.
Besides, we have one important note for piston pre-assembly. We fit wear rings and back-up rings correctly into their matching grooves, and stagger their split openings during installation. This stops the rings from twisting while assembling. After we finish pre-assembly, we check the installed seals to confirm none of them are twisted. Then we fit the piston into the cylinder barrel and test the sliding movement by hand, pushing it back and forth. We make sure it moves smoothly with no sticking. This prevents motion problems when we fully put the whole cylinder together.
2. Piston Rod Insertion into Guide Sleeve and Piston Assembly Fitting
For the second step, we insert the piston rod into the guide sleeve and then fit the piston assembly. First, we clean the piston rod thoroughly, and apply a thin coat of assembly lubricant compatible with the seals onto the rod surface. This oil film blocks air, moisture and sweat from our hands, preventing the hard chrome layer on the piston rod from rusting during assembly. It also helps the piston rod slide smoothly into the guide sleeve and keeps the seals on the guide sleeve from scratching the chrome surface. When we feed the piston rod through the guide sleeve, the rod passes the lips of the wiper seal and main seal one after another. So we fit a protective sleeve over the front end of the piston rod. It creates a smooth transition. This prevents the pre-installed lips of the main seal and wiper seal from folding over or getting scratched by the sharp edge of the rod tip.
After inserting the piston rod into the guide sleeve, we fit the pre-assembled piston assembly per the drawing. That means we mount the pre-assembled piston assembly onto the piston rod tip. First, we slide the piston over the rod tip and push it along the rod until it reaches the limit shoulder on the rod and will not go any further. When we confirm the position is correct, we use a torque wrench to tighten the piston lock nut to the torque value specified on the drawing. This firmly clamps and secures the piston.After tightening, we check to make sure the piston outer ring and piston rod are concentric. We also verify that the piston’s radial runout stays within the limits on the drawing. Radial runout is the swing of the piston outer ring when we turn the piston rod. If runout exceeds the limit, the piston will tilt while the cylinder works. This causes one-sided wear on the piston seals and wear rings.
3. Loading the Piston Rod Assembly into the Cylinder Barrel
For the third step, we load the piston rod assembly into the cylinder barrel. First, we inspect the inner wall of the cylinder barrel. We make sure it is clean and free of burrs, iron chips or rust. Then we apply assembly lubricant compatible with the seals to the inner wall. This cuts down friction as we push the piston into the barrel and protects the seal rings.Next, we slowly push the piston rod assembly into the cylinder barrel. While pushing, we watch the chamfer, threads and oil ports at the barrel end. We prevent these areas from scratching the seals. We also keep the piston rod centered with the cylinder barrel. This keeps the seals on the piston outer ring from getting squeezed on one side and folding over their lips.
While pushing, we also keep steady pushing force. If we feel any binding, we do not force the push, because this may mean the seals at the piston edge are caught on the sharp edges of the barrel opening or oil port. In other words, the piston jams on one side. If we keep pushing hard here, the seals will get cut, and the piston will tilt from uneven force, and its metal edge will scratch the inner wall of the cylinder barrel. When we finish pushing it into position safely, we do a short manual push-and-pull test. If it slides smoothly by hand, the piston seals have no obvious damage from insertion.
4. Cylinder Head Installation with Lock Nuts or Tie Rods
For the fourth step, we fit the cylinder head. We use lock nuts or tie rods according to the cylinder design to secure the cylinder head to the barrel. This keeps the connection firm so it will not come loose while working. Generally, for small and medium cylinders with threaded construction, we use lock nuts to secure the cylinder head. For heavy-duty tie-rod style cylinders, we use tie rods instead.
Before assembly, we clean the cylinder head and the threaded areas used to fasten the cylinder head. We remove iron chips and debris from the threads. Then we fit the main piston rod seal, O-rings and back-up rings onto the cylinder head one by one. After we fit all the seals, we slide the cylinder head over the piston rod and seat it against the front end of the cylinder barrel. Next, we tighten the nuts or tie rods to the torque values required per the drawing and process requirements, making sure all fasteners get even force. If the drawing calls for thread locker, we apply it on the thread flanks before tightening the fasteners. This locks the threads and prevents threaded joints from loosening with long service.
After assembly, we check the concentricity between the cylinder head and cylinder barrel. We also check the fitting gap between their end faces to make sure the cylinder head is not off-center. We record the torque readings from our torque wrench. We also add anti-loosening witness marks. Half the mark goes on the side of the nut, and the other half extends onto the barrel or tie rod. This lets technicians quickly check if nuts or tie rods have shifted during later maintenance.
5. Port Connector and Dust Cover Installation
For the fifth step, we fit the port connectors, and install dust covers according to the cylinder configuration. First, we clean the port connectors thoroughly. We apply thread sealant or wrap PTFE tape on the connector’s external threads following process requirements. This seals the thread gaps and stops hydraulic oil leaks. We pay extra attention during this step. We apply sealant only on the connector’s external threads, not on the inner bore. We also make sure no sealant or PTFE tape fragments drop into the cylinder oil passages. If debris gets into the oil circuit, it travels with the hydraulic oil and scratches the seals and cylinder barrel inner walls. This can cause the cylinder to leak.
After we finish thread sealing, we tighten the port connectors straight away. We torque them to the values specified on the drawing. If torque is too low, the connector may loosen and leak oil. If torque is too high, it can crack the port threads and damage the cylinder body. Next, we screw port plugs onto the port connectors. The plugs seal off the ports, keeping dust and contaminants out of the cylinder while preventing internal oil leakage.
After assembling the port connectors, we install the dust covers. After it is fitted, we fasten the dust cover with hose clamps or retaining rings. Then we pull the dust cover gently by hand and verify it will not shift or come off. This keeps outside dust and contaminants out of the cylinder to prevent secondary contamination.
After the cylinders are assembled, they will be sent to the test bench for testing.
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