Hydraulic Cylinder Repair: Big or Small, We Fix Them All

They raise booms, steer equipment, tilt buckets, move outriggers, lift forks, clamp tooling, fold implements, and keep machines working under load every day.

And sooner or later, they leak.

At Mondak Equipment, we repair hydraulic cylinders from small steering and lift cylinders all the way up to large industrial, crane, oilfield, construction, aerial, agricultural, and material-handling cylinders.

Sometimes they just need seals.

Sometimes they need a little more attention.

Either way: big or small, we fix them all.

Most Leaking Cylinders Just Need Resealed

A leaking cylinder does not automatically mean something major is wrong.

A lot of the time, the seals are simply worn out.

Rod seals harden. Wipers wear down. O-rings flatten. Piston seals eventually lose their ability to hold pressure. After thousands of cycles, that is normal.

If the rod, barrel, piston, and gland are still in good condition, a new seal kit may be all the cylinder needs.

We disassemble it, clean it, inspect the components, install the correct seals, put it back together, and get it back to work.

No reason to turn a simple reseal into a major rebuild.

What Is Actually Inside a Hydraulic Cylinder?

A cylinder may look like a tube with a shiny rod sticking out of it, but quite a bit is happening inside.

The main components include:

• Cylinder barrel
• Piston
• Piston seals
• Wear or guide rings
• Chrome rod
• Gland or cylinder head
• Rod seal
• Wiper or scraper
• O-rings and backup rings
• Extend and retract ports

Hydraulic pressure acting on the piston creates linear force.

Pressure entering the cap end pushes the piston and rod outward. Pressure entering the rod end moves the piston back and retracts the rod.

Simple idea. Serious force.

Every Seal Has a Job

The seals inside a cylinder are not all doing the same thing.

Rod seals keep hydraulic oil from leaking past the rod.

Wipers and scrapers help keep dirt, mud, dust, and water from being dragged into the cylinder.

Piston seals prevent pressure from bypassing around the piston.

Wear and guide rings support the piston or rod and help prevent metal-to-metal contact.

O-rings and backup rings seal stationary joints and support sealing elements under pressure.

When these components wear, a cylinder may leak, drift, bypass internally, or lose force.

Hercules Sealing Products Distributor

A cylinder repair can come to a halt over one seal.

That is why having access to the right sealing products matters.

Mondak Equipment is a Hercules Sealing Products distributor, giving us access to a huge range of:

• Rod seals
• Piston seals
• Wipers and scrapers
• O-rings
• Backup rings
• Wear rings
• Metric seals
• Complete seal kits
• Specialty hydraulic sealing products

And turnaround is fast.

If we have the Hercules order in by 7:00 PM, many seals can be here the next day.

But the bigger advantage is what happens when the seal is not sitting on anybody's shelf.

Odd Size? Metric? Obsolete? Hercules Can Make It.

Not every cylinder uses a common seal.

We see older equipment, imported machinery, metric cylinders, specialty equipment, custom-built cylinders, and machines where the original manufacturer no longer supports the parts.

Sometimes you take a cylinder apart and discover a seal size or profile that simply is not available off the shelf.

That does not necessarily mean the cylinder is done.

If Hercules does not stock the odd-size or metric seal we need, they have the capability to manufacture sealing components to the required dimensions.

That gives us another option when dealing with:

• Odd seal dimensions
• Metric cylinders
• Uncommon profiles
• Obsolete seal kits
• Imported equipment
• Older industrial cylinders
• Custom or specialty applications

Instead of replacing an otherwise repairable cylinder because one unusual seal cannot be found, we can work toward having the sealing component made for the application.

For older and specialty equipment, that capability can be a big deal.

No Part Number? Not Necessarily a Problem

Not every cylinder arrives with a readable tag and an easy OEM seal-kit number.

Some have been rebuilt several times. Some came from manufacturers that are long gone. Others may have no identification at all.

In those situations, we can work from the cylinder and seals themselves.

Rod diameter, bore diameter, groove dimensions, seal profile, width, and cross-section help us determine what belongs in the cylinder.

Sometimes we find an off-the-shelf Hercules seal.

Sometimes we find a complete kit.

And if it turns out to be something unusual, custom-manufactured sealing components give us another way to keep the repair moving.

When a Seal Kit Is Not Enough

Most cylinder repairs are straightforward.

But occasionally we take one apart and find something that would destroy a fresh set of seals.

That is when the repair goes further.

Scored Barrel?

The piston seals travel along the cylinder bore every time the cylinder cycles.

If the bore has light scoring, glazing, rust, or surface damage, honing may restore the surface and give the new seals a proper place to run.

Not every barrel needs honed.

If it is good, we leave it alone.

Bad Rod?

A damaged rod can chew up a new rod seal quickly.

We commonly see rods that are:

• Pitted
• Scratched
• Rusted
• Gouged
• Bent
• Damaged at the threads or rod end

If a rod is beyond practical repair, Mondak Equipment can manufacture a new one.

That can save an otherwise good cylinder, especially when a complete replacement is expensive, obsolete, or unavailable.

A Dry Cylinder Can Still Be Bad

A hydraulic cylinder does not have to leave a puddle on the floor to have bad seals.

When a piston seal bypasses internally, oil moves from one side of the piston to the other instead of doing useful work.

The cylinder may:

• Drift
• Move slowly
• Feel weak
• Lose lifting force
• Fail to hold position
• Work unloaded but struggle under load

Sometimes the most important seals in the cylinder are the ones you cannot see from the outside.

Counterbalance Valves Can Fool You

Many cylinders on cranes, aerial lifts, telehandlers, booms, outriggers, and other load-holding applications have counterbalance or load-holding valves mounted on or near the cylinder.

Their job is to help control the load.

When a heavy boom is lowering, for example, gravity wants to drive the cylinder. The counterbalance valve meters oil leaving the loaded side so the movement stays controlled.

When one starts sticking or leaking internally, it can make a good cylinder look bad.

Symptoms can include:

• Boom drift
• Slow lowering
• Jerky movement
• A function that will not lower
• Excessive heat
• Poor operation in one direction

Sometimes the problem is not inside the cylinder.

It is bolted right to it.

Not Every Slow Cylinder Needs a Rebuild

"The cylinder is slow" does not automatically mean the cylinder is bad.

A slow or weak hydraulic function can also come from:

• Low pump flow
• Restricted hose
• Plugged filter
• Worn control valve
• Sticking spool
• Relief-valve problems
• Low pilot pressure
• Counterbalance-valve problems
• Internal leakage elsewhere in the system

Good hydraulic troubleshooting is about figuring out where the pressure and flow are actually going.

Replacing parts until the machine works gets expensive.

If It Keeps Blowing Seals, Something Else Is Going On

A cylinder needing a seal kit after years of service is normal.

A cylinder blowing the same seal every few weeks is not.

Repeated failures can point toward:

• Bent rod
• Damaged chrome
• Scored barrel
• Worn gland
• Side loading
• Misalignment
• Contamination
• Excessive heat
• Pressure spikes
• Incorrect seals

At that point, another seal kit may only buy time.

We want to know why it keeps failing.

Cylinders From Just About Everything

We repair hydraulic cylinders used on:

• Oilfield equipment
• Workover rigs
• Hydraulic catwalks
• Iron roughnecks
• Cranes
• Boom lifts
• Bucket trucks
• Telehandlers
• Forklifts
• Excavators
• Wheel loaders
• Dozers
• Agricultural equipment
• Trucks and trailers
• Rail equipment
• Industrial machinery
• Specialty equipment

Some cylinders can be carried under one arm.

Others require a forklift just to get them through the shop.

The basic process is still the same:

Take it apart. Inspect it. Fix what is worn. Put it back together correctly.

Hydraulic Cylinder Repair at Mondak Equipment

Our cylinder repair capabilities include:

• Resealing and seal kits
• Complete cylinder rebuilds
• Cylinder honing
• New rod manufacturing
• Rod inspection and repair
• Piston and gland inspection
• Wear and guide ring replacement
• Seal identification
• Hercules seal sourcing
• Custom odd-size and metric seal manufacturing through Hercules
• Counterbalance valve troubleshooting
• Load-holding valve troubleshooting
• Hydraulic system diagnostics

Most importantly, we match the repair to the problem.

If it just needs seals, we reseal it.

If the barrel needs honed, we hone it.

If the rod is bad, we can make another one.

If the cylinder is fine and the counterbalance valve is causing the problem, we find that too.

And if the seal is some oddball metric size that nobody has on the shelf, our relationship with Hercules gives us the ability to have it manufactured.

Big or Small, We Fix Them All

Leaking?

Drifting?

Bent rod?

Scored barrel?

Oddball metric seal nobody can find?

Bring it to Mondak Equipment.

As a Hercules Sealing Products distributor, many seal orders placed by 7:00 PM can be here the next day, and when an unusual size is not available, Hercules can manufacture sealing components for the application.

Big or small, we fix them all.