Servo valves
Denison and Parker Denison electrohydraulic servo valves. Pilot stage cleaning and trim, spool service, coil rebuild, seal replacement, and bench testing on the hydraulic stand.
NC Servo Technology - Westland, Michigan
734-326-6666
Independent Repair Shop. Not Parker. Not Denison.
Third-Party Repair of Denison Hydraulics Valves & Controls
Independent third-party repair of Denison Hydraulics and Parker Denison hardware: servo valves, proportional directional and flow control valves, and electronic control cards. Coverage spans both pre-2003 Denison Hydraulics legacy units and current Parker Denison production. Backed by a 19,000+ unit in-house inventory we pull aftermarket and donor parts from. NC Servo is not affiliated with Parker Hannifin or Denison. Working on this kind of hardware since 1975.
Pre-2003 + post-2003
Both Denison Hydraulics legacy hardware and current Parker Denison production.
Three product types
Servo valves, proportional valves, and electronic control cards under one roof.
One-year warranty
Standard on parts and workmanship for Denison repairs and rebuilt units.
Acquisition Timeline
Denison Hydraulics, then Parker Denison, then Parker
The Denison name has gone through three eras. The hardware in your machine probably wears the nameplate from whichever era it was built in. We work on hardware from all three.
Pre-2003
Denison Hydraulics
Standalone American hydraulic valve and pump maker. Servo valves, proportional valves, and electronic controls shipped under the Denison Hydraulics name. This is where the legacy part numbers come from.
2003
Parker acquires Denison Hydraulics
Parker Hannifin folds Denison into its Hydraulics Group. Hardware shipped through this transitional period typically carries "Parker Denison" branding on the nameplate.
Post-2003
Parker Denison and Parker
Newer hardware carries Parker on the label, with Parker Denison still in use on continuing valve and control lines. Same family of products, updated part numbers, same spool and pilot work on the bench.
Today
Both eras still in service
20+ years after the acquisition, plenty of pre-2003 Denison Hydraulics valves are still running on machines and need work. We service those alongside current Parker Denison units.
Service Coverage
What NC Servo does with Denison hardware
Denison's lineup is unusual for a single brand: servo valves, proportional valves, and electronic control cards all show up here. We open each unit, find what failed, and rebuild it at the component level using parts from inventory or pulled off donor units.
Proportional valves
Proportional directional control valves and proportional flow control valves. Coil work, spool service, driver-card checks where the model has onboard electronics, and full functional verification.
Electronic control cards
Denison electronic control cards and electro-hydraulic system controllers. Circuit diagnostics, component-level board work, and signal verification under load on the electronic test bench.
Denison Coverage
What comes through the door under the Denison name
We are a small repair shop, not a Denison or Parker distributor. The categories below are simply the ones that come through often enough to be familiar. If your part number is not in this list, send it anyway. We work on what we can.
Denison Hydraulics legacy
Pre-2003 servo and proportional valves with the original Denison Hydraulics nameplate. Discontinued lines kept running with donor parts pulled from inventory.
Parker Denison transitional
Hardware from the years right after the 2003 acquisition. Both names show up. Same internals as the Denison-era units in many cases.
Current Parker Denison
Servo valves and proportional valves still shipped under the Parker Denison name in current production hydraulic lines.
Electronic control cards
Denison electronic cards and electro-hydraulic controllers across both eras. Bench-tested under load with proper signal verification.
Common Faults
What usually shows up on a Denison repair
A description of the symptom helps the diagnosis, but a part number is often enough. The categories below cover the kinds of trouble that come in across Denison servo valves, proportional valves, and control cards.
| Pilot stage and torque motor | Pilot-pressure null shift, torque motor coil burnout, flapper damage, contamination in the pilot path, or wear on the feedback wire on servo valves. |
|---|---|
| Spool and body | Spool wear, contamination scoring, sticky spool action, internal leakage past the spool, or seal failure on directional and flow control bodies. |
| Coils and driver electronics | Burned proportional coils, failed onboard driver cards, position-feedback faults, or open windings on the pilot stage. |
| Control card faults | Power-supply failures, blown output stages, signal-conditioning drift, or bad pots on Denison electronic control cards and electro-hydraulic controllers. |
Repair Path
From part number to ship-back
Most Denison jobs follow the same four steps. Lead time varies because some repairs need parts pulled off a donor unit or a control card pulled off the electronics bench, so we only commit to timing once a tech has the unit in hand.
Get in touch
Phone or email with whatever you have on the unit: a Denison or Parker Denison part number, a serial number, or a photo of the nameplate.
Bench review
Once the unit arrives, a tech opens it, inspects internals or board condition, and runs it on the hydraulic stand or electronic bench to confirm what failed.
Cost & approval
We call back with the cost and a rough turnaround. Nothing happens without your sign-off.
Repair, test, ship
Failed components are replaced from inventory or off donors, the unit is verified under load, and it ships back to you.
Bench Verification
Each Denison unit gets verified before ship
Repaired Denison valves are checked on the hydraulic test stands. Control cards are tested under load on the electronic bench. Flow, pressure gain, response, null, and signal output are all verified against documented procedures for the family.
- Flow characterization across the operating range for the valve.
- Pressure gain and step-response measurement against documented procedures.
- Internal and external leakage checked after seal and spool work.
- Electronic cards bench-tested under load with proper signal verification.
Inventory & Parts Pool
A 19,000+ unit pool with Denison hardware in it
NC Servo's in-house inventory holds over 19,000 valves and drives accumulated since 1975, including a steady share of Denison and Parker Denison hardware from both eras. That pool is where the shop pulls aftermarket parts and donor components for older Denison Hydraulics units that Parker no longer services.
- Aftermarket and donor parts for Denison Hydraulics and Parker Denison valves and cards.
- If we have a rebuilt match for your part number, trade in your old unit for a discount on the rebuilt.
- No match on the shelf? We can suggest a comparable Denison, Parker Denison, or cross-brand option, or repair yours.
- Rebuilt valves and cards carry the same 1-year warranty as a fresh repair.
Repair Scope
Where the line is on a Denison repair
NC Servo works on the valve and card hardware: the body, spool, pilot stage, coils, control-card board components, and connectors. Hydraulic system design, fluid selection, and getting the unit back on the machine stay with your team or your installer. We do not repair Denison hydraulic pumps.
- Internal valve work: spool service, seal replacement, pilot stage cleaning, coil rebuild.
- Electronic card work: component-level board repair, signal verification, output stage rebuild.
- System pressure setup, schematic decisions, and pump-side work remain on your side.
- Putting the unit back on the machine follows your normal startup process.
More on Denison Repair
Related pages and brands
Denison hardware often shares a machine with valves and electronics from related brands. The pages below cover related coverage, the Parker side of the family, and other valve work.
Valve repair hub
The full range of servo and proportional valve repair NC Servo handles, across the brands that come through the shop.
Industrial valve repair
How the shop approaches industrial hydraulic valve work in general, including exchange and donor-parts options.
Parker brand page
The other side of the Denison story. Useful when your unit is labeled Parker or Parker Denison rather than Denison alone.
Repair vs replace
When component-level repair makes sense versus buying new or rebuilt.
Denison or Parker Denison unit down?
Give us a call with whatever is on the nameplate, even if it just says Denison from before the Parker era. We will check the shelf, and if we have a rebuilt match you can swap your old one for a discount. If we do not, we can suggest a comparable valve or repair the one you have.
FAQ
Common questions about Denison repair
A few things customers ask before sending a unit in. Anything not covered, give us a call at 734-326-6666.
Is NC Servo affiliated with Parker Hannifin or Denison?
No. NC Servo Technology is an independent, third-party repair facility and is not affiliated with, authorized by, or endorsed by Parker Hannifin, Denison, or any related entities. All Parker and Denison trademarks are the property of their respective owners.
Do you service both Denison Hydraulics legacy and current Parker Denison hardware?
Yes. Parker acquired Denison Hydraulics in 2003. Hardware shipped before that carries the Denison name; newer units carry Parker, and transitional units carry Parker Denison. We work on either. Send the part number off the nameplate and we will tell you what we have.
Which Denison products are in scope?
Servo valves, proportional directional control valves, proportional flow control valves, and electronic control cards / electro-hydraulic system controllers. We do not repair Denison hydraulic pumps.
Can NC Servo recover programs from a failed Denison control card?
Most failures are hardware, and the unit comes back working with its program intact. Corrupted programs are rare; if one is already corrupted before the unit reaches us, that's the one thing we can't recover.
How long does a Denison repair take?
It varies. NC Servo is a small independent shop, and lead time depends on the unit, what is wrong with it, and whether parts have to come off a donor. Give us a call once the valve or card ships in, and we can give a current estimate after a tech has looked at it.
What if the unit is beyond economic repair?
If the valve or card is not fixable, we will let you know and help source a replacement: a rebuilt match if we have one on the shelf, or a comparable Denison, Parker Denison, or cross-brand alternative.
What is the warranty on a Denison repair?
One year on parts and workmanship for repairs and rebuilt units. Standard exclusions apply for contamination, improper installation, and out-of-spec operation. Flushing and filtering the hydraulic system before reinstalling a repaired valve is recommended.