Critical Details of Hydraulic Cylinders

Hydraulic Cylinders

Hydraulic cylinders are a vital component of hydraulic systems, and thus reliability of hydraulic cylinders is crucial to the operation of your hydraulic system.  That is why using high quality hydraulic cylinders can reduce down time, loss of costly hydraulic fluid, and increase safety.  Some of the more common hydraulic cylinder defects are internal leakage, leakage around the rod seal, and broken, bent or otherwise damaged materials. 

So how can using a high quality cylinder manufactured from premium materials reduce these defects?

When you look at a hydraulic cylinder, they appear to look the same from manufacturer to manufacturer.  However, there is more to a cylinder than meets the eye.  A basic hydraulic cylinder consists of a tube (sometimes referred to as a barrel), a rod, a piston, and a head.

Starting with the tube, Montana Hydraulics LLC starts with a high quality alloy specifically designed for use in hydraulic cylinders.  While a lot of companies buy pre-honed tube, we prefer to purchase tube that is suitable to hone.  We weld the ports and other components to the cylinder before it is honed.  This ensures that the customer is getting a cylinder honed to the proper finish, and that when the weld distorts the tube; the honing process will finish the tube round.  The retract ports are finished by hand to ensure that seals are not damaged during assembly.

The rod is another critical component.  Montana Hydraulics uses only IHCP (induction hardened chrome plated) cylinder rod.  A lot of manufacturers use chrome plated rod.  So why use IHCP? Three words:
- Durability
   - Toughness
   - Longevity 
The cylinder is often exposed on a hydraulic cylinder, and especially on construction equipment, will see a lot of abuse.  Rocks and debris are beating on the rod day after day, and so the rod gets damaged.  Little nicks, chips and dings start to appear, and soon, this results in the failure of the rod seal.  As the rod passes across the rod seal, chips, nicks and dings wear and tear at the seal.  To understand how critical the surface of a rod is to a seal, consider the recommended finish for a rod.

Surface finish is measured in Ra, Rz, and RMS  (Rq), with the most common scale in hydraulics being Ra.  The measure of a surface finish, Ra, is defined as the arithmetical mean deviation of the assessed profile.  In simple terms, it is the measure of peaks and valleys in the surface over a defined distance.  This surface is critical in the longevity and sealing properties.  If the surface is too rough, oil is allowed to pass under the seal through the “valleys”, thereby causing oil to leak by the seal.  If the surface finish is too smooth, no oil is passed under the seal at all, thereby increasing the wear of the seal.  Ideally, a very small amount of oil should pass under the seal to allow for lubrication of the seal, but not enough that there is leakage.  The typical recommended surface finish of a cylinder rod is:  Ra = 4 to 12 μin (0.1 to 0.3 μm).  This is a very fine finish, considered to be smooth.  If a rod has a lot of dings, scratches and dents, this will increase the amount of oil that is passed under the seal.  Over time, as the defects pass across the seal, they increase the wear of the seal, leading to premature failure of the seal.

This is one of the reasons that Montana Hydraulics uses IHCP, versus chrome plated rod.  IHCP is case hardened, so the surface is more durable, and typically has of HRc 50 minimum (Rockwell hardness C), while chrome plated rod has a HRc 69 minimum hardness.  What this means for the end user of the hydraulic cylinder is increased rod seal life, reduced leakage, and less down time.

Another important aspect of the ability of the rod seal is the cylinder head in which it is contained.  The diametrical clearance of the head to the rod is very critical, because if there is too much clearance between the rod and the inside diameter of the head, the seal will extrude and thus fail.  Some manufacturers have a “loose” clearance, because tighter clearance translates to higher machining costs.  Over the life of the cylinder, the rod has a tendency to wear against the side of the head, and thus increasing the clearance.  If a cylinder is manufactured to the maximum allowable clearance, then as the cylinder wears it becomes un-repairable with a new seal.  Simply stated, better tolerances lead to longer cylinder life.

In order to reduce the wear on the cylinder head, Montana Hydraulics uses premium materials, and wear bands in the cylinder head.  Wear bands act as medium between the head and the rod, so the wear band, which is replaceable, wears instead of the head.  Also, because wear bands, when used in oil, have excellent wear characteristics.  With wear bands in place, the rod doesn’t make contact with the inside diameter of the head.

A high quality hydraulic cylinder is always a wise investment, but what about repair of existing hydraulic cylinders?  Hydraulic cylinders are expensive, and so it makes sense to repair cylinders when needed instead of replacing.  One common misconception is that welded cylinders can’t be repaired.  This is simply not true.  A reputable hydraulic shop with qualified machinists, welders and hydraulic technicians, such as Montana Hydraulics, can easily repair welded hydraulic cylinders.

After years of service, everything has a tendency to wear out, and hydraulic cylinders are no exception.  It is generally thought that a simple seal replacement will repair a leaking cylinder.  For a lot of repair work, this is true, but many times seals fail because of other mechanical defects.  If the inside diameter of the head has excessive wear, installing a new seal will not fix the problem for long.  Having a qualified technician disassemble and inspect a cylinder will save a repeat trip to the repair facility.  Because a hydraulic cylinder is a precision component, all of the clearances are critical.  If the tube is scratched, dented or otherwise damaged, new piston seals will not repair the problem. 

Montana Hydraulics has the ability and know how to re-rod, re-tube, build new pistons and heads to ensure that hydraulic cylinders are repaired correctly the first time, and it is this expertise that allows us to warranty repaired cylinders for one full year (if the customer approves all of the repairs recommended by Montana Hydraulics).  Even when new components are needed for a cylinder it is still cheaper than replacing most quality OEM hydraulic cylinders.  From the correct torque on a piston nut, to the correct clearances of the cylinder, why risk down time and multiple trips to repair facilities, when having it done right and fully tested is like installing a new cylinder?

So when you are looking at purchasing new custom hydraulic cylinders, or when a repair is needed, think about choosing Montana Hydraulics LLC.  We have the experience, knowledge and tools to complete the job correctly.

 - Article Written By Gerald, Montana Hydraulics LLC

Questions Regarding Our Hydraulic Cylinder Capabilities?
Give us a call at 877.449.3464 or send us a message through the contact page, and allow us to demonstrate our commitment to superior customer service and our years of experience in Hydraulic Cylinder manufacturing, repair, design and expertise.

Hydraulic Cylinders

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