Masoneilan 4200P Pneumatic Valve Positioner
Overview
The Masoneilan 4200P is a pneumatic positioner from Baker Hughes that compares a 20-100 kPa control signal with the real position of a valve stem or shaft and corrects the air sent to the actuator. It is built around a durable cast aluminum cover, a single-piece input chamber and pilot, a built-in four-sided solid cam, a pilot valve that saves air and a multifunctional pilot relay. Direct or reverse action and left or right mounting are selected at installation, and the unit weighs about 1.1 kg.
Seven Star LLC is the trusted supplier for Masoneilan in the Sultanate of Oman and supplies the Masoneilan 4200P with actuators and valves, as well as for replacement on installed Masoneilan assemblies. Our Muscat team can confirm the action, cam and bracket required before an order is placed.
Operating Principle of the Masoneilan 4200P
In the single-action Masoneilan 4200P an input signal enters the input chamber and moves a damper relative to a nozzle. A change in nozzle back pressure drives the pilot relay, which delivers output pressure to the actuator. The movement of the actuator is returned through a drive rod, levers and the cam to a feedback spring, and the positioner settles where spring force balances the input force. In normal mode output pressure rises as signal pressure rises, and a reverse mode is available.
The dual-action positioner uses the same balance but supplies two outputs, so it can drive double-acting cylinders. A seat position regulator adjusts the equalizing pressure of the output, which is set to roughly 75 percent of supply pressure during loading and normally needs no adjustment. A unique range adjustment mechanism lets the span be changed in half-division steps without replacing the spring, which also supports 1/2 split-range service.
Engineering Design of the Masoneilan 4200P
The frame and cover are cast aluminum with alumite treatment. A drip-proof outlet lid fits the outlet port at the rear, and the exhaust cover has a drain hole whose direction can be changed by loosening a screw if it would otherwise face upward. Supply, input signal and output connections are marked as SUPPLY, INSTR and OUTPUT1. The manual specifies that connections be made with Loctite 577 or similar rather than sealing tape, because tape fragments can block the relay and cause malfunction.
For linear valves the Masoneilan 4200P is fitted with an adapter plate and bracket and a feedback lever that must be parallel to the plate when the actuator is at 50 percent stroke. For rotary valves a coupling is installed on the shaft. The standard version works from -20 to +83 degC, and a low-temperature execution (L) is rated -50 to +60 degC. The manual also covers storage and handling: keep the positioner away from rain, keep the connection plugs in place until installation, supply clean, dry air free of chemicals, organic solvent-based synthetic oil and corrosive gas, and fit a dehumidifier or aftercooler if the air carries moisture. These rules matter in the hot, humid coastal climate of the Gulf of Oman, where wet instrument air is a common cause of positioner faults.
Key Features
These are the points that explain why the Masoneilan 4200P remains in use on pneumatic loops:
- The Masoneilan 4200P has a built-in four-sided cam that provides a linear characteristic, with an equal-percentage cam as an option.
- Direct and reverse action and left or right mounting are selected without changing parts.
- A pilot valve and multifunctional relay save instrument air.
- Span can be adjusted in half-division steps without replacing the spring, which supports split-range operation.
- Single-action and dual-action versions cover spring-return and double-acting actuators.
- The cast aluminum frame and cover are compact and light at about 1.1 kg.
- Vibration resistance is specified at 1 percent for 1 G over 10 to 200 Hz.
- Rubber seals, relay and damper are treated as parts with a limited service life of about five years in the periodic inspection table.
Industrial Applications
The Masoneilan 4200P suits plants that run pneumatic control loops on globe, rotary and butterfly valves, where a simple air-signal positioner without electronics is preferred or where hazardous-area rules make a pneumatic device attractive. Typical Omani users are utilities, water treatment, refining and gas processing sites around Sohar, Duqm and Salalah that maintain mixed fleets of older Masoneilan valves and actuators.
In Oman and the GCC, Seven Star LLC supplies the Masoneilan 4200P with related positioners such as the Masoneilan SVI3 digital valve positioner and the Masoneilan SVI-3112F121 SVI FF digital positioner, and we can advise when upgrading the Masoneilan 4200P to a digital positioner makes sense for your loops. The manual’s periodic inspection table, which lists frame, cover, relay, nozzle and damper checks, is a useful basis for a preventive maintenance plan.
Related published Masoneilan pages: Masoneilan Type 87/88 spring-diaphragm actuators.
Technical Specifications
The table lists the published data for the Masoneilan 4200P from the 2024 Baker Hughes manual.
| Parameter | Specification |
|---|---|
| Model | Masoneilan 4200P pneumatic positioner, single-action and dual-action |
| Input signal | 20-100 kPa standard; 20-60 kPa and 60-100 kPa options |
| Incoming air pressure | 130-700 kPa |
| Movement (stroke) | 12-50 mm standard; 40-100 mm option |
| Air connection | Rc1/4 (NPT 1/4 option); gauge ports NPT 1/8 |
| Ambient temperature | -20 to +83 degC; low-temperature version -50 to +60 degC |
| Linearity | Plus or minus 1.5 percent (single-action); plus or minus 2.0 percent (dual-action) |
| Hysteresis | 1.0 percent |
| Repeatability | 0.3 percent (single-action); 0.5 percent (dual-action) |
| Sensitivity | 0.2 percent (single-action); 0.5 percent (dual-action) |
| Air flow | 5 L/min (norm) at 140 kPa (single-action, 50 percent output) and 10 L/min at 400 kPa (dual-action) |
| Maximum throughput | 60 L/min (norm) at 140 kPa single-action; 140 L/min (norm) at 400 kPa dual-action |
| Material | Cast aluminum frame and cover, alumite treated |
| Weight | Approximately 1.1 kg |
| Pressure gauges (optional) | 0-200, 0-400 and 0-1000 kPa; units psi, MPa or bar |
Related Masoneilan positioners include the Masoneilan 4700P/4800P pneumatic positioner, Masoneilan 8013 electro-pneumatic cam positioner and Masoneilan 4411 electro-pneumatic transducer.
Request a Quote for Masoneilan 4200P
To request pricing or technical support for the Masoneilan 4200P, send a formal RFQ to the Seven Star LLC instrumentation division with the actuator type and stroke, the signal range, the required action and cam, and the supply pressure. We can confirm the numbering code, advise on availability and lead time and supply the Baker Hughes manual linked on this page. In Oman and the GCC, Seven Star LLC supplies genuine instruments with manufacturer documentation and local engineering support.
- Instruction Manual Masoneilan 4200P Positioner Instruction Manual Download
Masoneilan control valves and actuator series
The globe valve listing centers on the 21000 series, including the cryogenic version with extension bonnet, and the 41005 cage-guided series in high pressure, API 6A and VRT anti-cavitation executions. The 80385 and 80386 are three-way combining and diverting valves. Rotary products include the 35002 Camflex II and the 37002 MiniTork II butterfly control valve. Actuators cover spring-diaphragm, cylinder and rack-and-pinion designs, among them the 5A cylinder actuator for Camflex II. Masoneilan also makes pressure regulators, SVI digital valve positioners and displacer-type level instruments, and offers Lo-dB trim for noise control.Where Masoneilan valves are used
Throttling duty on steam, hydrocarbons, gas and water is the daily work of these valves: feedwater and steam conditioning in power plants, separator and compressor loops in gas processing, high pressure drop letdown, cryogenic service in LNG and air separation, and general flow, pressure and level control in refineries and chemical plants.Ordering Masoneilan valves and spare parts: what we need
For spare parts the serial number is decisive, since the factory record behind it lists trim, materials and actuator. Send a clear nameplate photo with serial number, model number, size and pressure class. For a new valve add the process data: fluid, inlet and outlet pressure, temperature, minimum, normal and maximum flow, required leakage class, fail position, air supply and control signal.Browse Masoneilan products by category: Control Valves, Valve Actuator, Regulators, Valve Positioner, Level Transmitter.
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