Common Hydraulic Cylinder Terms

  • Stroke – the travel of the cylinder, extended length (pin to pin center) minus the retracted length (pin to pin center).
  • Retract – the length pin to pin center when cylinder is fully closed.
  • Rod/Ram/Cylinder Shaft – the round device that moves in and out of the cylinder. The cylinder can be solid or hallow. The rod is usually plated or heat treated to provide better wear and corrosion resistance.
  • Bore – the inner diameter of the cylinder barrel.
  • Cylinder Barrel – The barrel is the cylindrical body of the cylinder. The barrel guides the piston and provides a sealing surface for the piston seal. The barrel is also the structural part of the cylinder that holds the ends in place.
  • Cylinder head gland (Stuffing Box) – The head gland or stuffing box is a cylinder component that serves more than one purpose. It retains the static and dynamic seals at the head end of the cylinder, it seals off at the end of the cylinders, it is the support or guide for the rod and it is the mechanical stop to keep the piston form falling out of the cylinder barrel.
  • Piston – the piston is a cylinder component that has multiple purposes. The piston retains the primary seal from the extend side of the cylinder and the retract side of the cylinder. It is the component that moves back and forth from the hydraulic oil. The piston is the mechanical means of connecting and moving the rod in and out of the cylinder as well as serves as a guide for one end of the piston rod.
  • Piston rod – The rod is also known as the cylinder shaft or ram. It is the round device that moves in and out of the cylinder. The piston rod can be solid or hollow. The rod is usually plated or heat treated to provide better wear and corrosion resistance.
  • Seals – Positive seal a seal that has the capability to seal with non-leakage. Static seal is a seal that does not move. Dynamic is a seal that seals a moving surface like a rod or a barrel.
  • Cushion – a cushion is an option on a cylinder that slows it down before the travel reaches the end of stroke. The cushion can be on the extend side of the cylinder or on the retract side or both. The cushion is utilized in a cylinder to keep it and the load from banging for the reduction in noise and or increase life of the apparatus it is moving
  • Port – cylinder ports are the means in which the cylinder is able to have fluid lines or conduits connected. O-ring Boss (SAE) Port is a port that has straight or parallel threads as well as an O-ring to seal the threads. Pipe Port the pipe threads are tapered threads that count on interference between the male and female threads to do the sealing. 4-Bolt Flange Port is a port that counts on 4 bolts to hold to two halves together. This type uses an O-ring to do the sealing. BSP is a British Standard Pipe Thread.

What is the difference between double acting and single acting cylinders?

  • Double-Acting (DAT) – have a port at each end, supplied with hydraulic fluid for both the retraction and extension.
  • Single-Acting (SAT) – hydraulic fluid enters through a port at one end of the cylinder, which extends the rod by means of area difference. An external force or gravity returns the piston rod.

What are some common causes of cylinder failure?

  • Side loading – Side loading is caused from the cylinder being misaligned which creates an unusual force on the piston rod. A side load of enough magnitude can result in tube scoring, piston rod and rod bearing wear, and seal failure.
  • Contaminated Fluid – Contaminated fluid can cause premature rod seal failure. Abrasive particles in the fluid can damage the seal and the piston rod surface, airborne contamination can be drawn into a cylinder by a faulty wiper seal. Contamination occurs in numerous ways, the most common is drawn in from oil or from the pump.
  • Rough or scored rod – Rough places on the rod damage the seals and reduce their normal life resulting in the necessity for frequent replacement.

What type of hydraulic cylinder mounts are available?

No Mount
No Mount
Rod Clevis Mount
Rod Clevis
Rod Eye Mount
Rod Eye
Spherical Rod Eye Mount
Spherical Rod Eye
Cross Tube Mount
Cross Tube Mount
Trunnion Mount
Trunnion Mount