Key Technical Specifications
| Parameter | Specification | Field Note |
|---|---|---|
| Input Signal | 4-20 mA DC | Standard industrial loop current |
| Output Type | Hydraulic Oil Pressure | Proportional to input current |
| Supply Pressure | Typically 150-2000 psi | Must match actuator requirements |
| Replaces | 8901-457, 8901-459, 9907-046 | Direct mechanical/electrical fit |
| Application | Steam/Fuel Valve Control | Turbines, Engines, Compressors |
| Mounting | Flange/Base Mount | Requires clean oil supply |
| Protocol | Analog Current Loop | No digital comms on this unit |
| Failure Mode | Fail-in-Place / Spring Return | Verify spring config for safety |
Product Introduction
I’ve pulled more of these off vibrating turbine decks than I care to count. The WOODWARD 9907-1106 is the CPC-II workhorse that turns your 4-20mA control loop into actual hydraulic muscle to move a steam valve. It’s not fancy; it’s a proportional transducer that takes an electrical command and spits out oil pressure with enough linearity to keep a 50MW turbine from tripping on speed deviation. If this thing fails, your valve slams shut or floats open, and you’re looking at an unplanned outage that costs more per minute than this part costs in a decade.Engineers stick with the CPC-II series because the mechanical tolerances hold up in hot, dirty oil rooms where digital electronics cook. The 9907-1106 specifically is the modern replacement for the old 8901-457 cast iron bodies that used to crack from thermal shock. It’s got a tighter spool fit and better internal filtration, but don’t get cocky; it still demands clean oil (ISO 16/14/11 or better) or the spool will stick and your load control will hunt like a drunk sailor. This specific revision is picky about supply pressure stability, so check your accumulator pre-charge before blaming the converter.
Quality SOP & Tech Pitfalls
The Lab Report:
I don’t trust “tested” stickers. Here is what actually happens on my bench:
- Visual/Counterfeit Check: Magnifying glass on the casting date codes and port threads. If the threads look rolled instead of cut, or the casting flash is sloppy, it’s a counterfeit.
- Bench Flow Test: Hooked up to a calibrated test stand with a digital pressure transducer. I sweep 4mA to 20mA and verify the pressure ramp is linear within ±1%. Any hysteresis >2% gets scrapped.
- Leak-Down Test: Pressurize the supply port, isolate, and watch the gauge for 5 minutes. If it bleeds down, the internal spool seals are shot.
- Coil Resistance: Fluke 115 across the input terminals. Should be within spec (usually ~250-300Ω for the coil + circuit). Open circuit = dead.
- Anti-Seal & Pack: Flush with dry nitrogen, cap the ports immediately, and bag it with desiccant. Moisture in a CPC is a death sentence.
The Engineer’s Warning:
⚠️ The “Clean Oil” Lie: Everyone says their oil is clean. It isn’t. I’ve seen 9907-1106 units fail in 3 months because the mechanic used a dirty funnel to top off the reservoir. A single 50-micron particle can score the spool, causing internal leakage that makes the valve drift. Install a 5-micron filter right before this unit. No exceptions.⚠️ The Spring Trap: These come in different spring configurations (Fail-Open, Fail-Close, Fail-In-Place). If you swap a Fail-Close unit into a Fail-Open application without checking, a power loss will blow your boiler or overspeed your turbine. Check the tag on the old unit before you unplug it. I once saw a guy install a “new” CPC without checking the spring, and during the first test trip, the valve stayed wide open because the spring was backwards. Ugly.
Installation & Configuration Guide
- Pre-Installation Safety: ⚠️ LOCKOUT/TAGOUT. Isolate the hydraulic supply and bleed the pressure to zero. Verify with a gauge. Take a photo of the old unit’s data tag and the electrical wiring. Do not trust your memory.
- Removal: Label the 4-20mA wires and supply/return lines. Unbolt the flange. Cap the supply line immediately. If you let system oil drain onto the floor, you’re buying a new filter element and cleaning up a mess.
- Installation: VERIFY THE TAG. Does the new 9907-1106 tag match the old one exactly? (Part number, spring code, pressure range). If it doesn’t, STOP. Call the supplier. Mount with new O-rings (never reuse old ones). Torque bolts in a star pattern to spec.
- Power-On & Testing: Open the supply valve slowly. Watch for leaks. Apply 4mA. Verify minimum pressure. Apply 20mA. Verify max pressure. Check for hunting. If the valve is oscillating, your supply pressure is too low, or the spool is sticky. Don’t tune the PID until you verify the hardware is solid.
Compatible Replacement Models
| Model | Status | Notes |
|---|---|---|
| WOODWARD 9907-1106 | ✅ Current Standard | Direct replacement for legacy CPC. Best availability. |
| WOODWARD 8901-457 | ❌ Obsolete | Cast iron body. Prone to cracking. Do not buy unless you have a specific legacy mount requirement. |
| WOODWARD 9907-1105 | ⚠️ Check Config | Same family, but verify pressure range and spring. Often interchangeable but verify tag. |
| WOODWARD CPC2000 | ❌ Hardware Mod | Digital upgrade. Requires new cabling, power supply, and control logic changes. Only do this during a full turbine overhaul. |
Frequently Asked Questions (FAQ)
Can I hot-swap this while the turbine is running?
Technically, yes, if your system has isolation valves and the control logic handles the “valve fail” state gracefully. Practically? Don’t. Hydraulic transients during the swap can spike pressure and damage downstream actuators. Plan a shutdown window. If you absolutely must do it live, ensure the bypass valve is open and the operator is ready to manually control load.My valve is hunting at 50% load. Is the 9907-1106 bad?
Maybe, but check the easy stuff first. Is your supply pressure stable? Is the oil temperature within range? Cold oil is thick and causes lag; hot oil is thin and causes leakage. I’ve seen hunting caused by a clogged 10-micron filter upstream. Swap the filter before you blame the converter.Does this need an external power supply?
No. The 4-20mA loop powers the internal coil. Do not connect 24VDC to the signal terminals unless the wiring diagram explicitly says so (some older 2-wire vs 3-wire configs get confused). Usually, it’s just a passive current loop.How do I know if it’s Fail-Open or Fail-Close?
Look at the data tag. It will say “Spring: FO” or “Spring: FC”. If the tag is gone, you have to bench test it: apply pressure, cut the signal, and watch which way the spool moves. Do not guess.Can I use standard hydraulic oil?
Yes, but it must be anti-wear (AW) hydraulic oil, ISO VG 32 or 46 typically. No turbine oil unless specified. Turbine oil has different anti-foam additives that can cause cavitation in the small orifices of a CPC. Check the manual for the exact viscosity grade.Why is the output pressure lower than expected at 20mA?
Your supply pressure is too low. The CPC can only output what it receives. If you need 1000 psi out, you need at least 1050-1100 psi in. Check your accumulator pre-charge and pump relief valve. I’ve wasted hours chasing a “bad CPC” that was just starved by a worn pump.Is the 9907-1106 compatible with the old 8901-457 mounting?
Generally, yes. The bolt pattern is the same. However, check the port depth. Some newer units have slightly deeper ports. If you use the old bolts, you might bottom out before sealing. Use the new hardware provided in the kit.
