KOSO EP800 Electro-Pneumatic Valve Positioner with 4-20mA for Precise Control

Product Overview

The KOSO EP800 Electro-Pneumatic Valve Positioner is a field-proven instrument designed for precise positioning of pneumatic actuator-operated control valves. It receives a 4-20 mA DC input signal from a controller and converts it into a proportional air pressure output to drive the valve actuator, ensuring accurate and repeatable valve positioning. The EP800 series is available in three main configurations: the EPA800 for single-acting actuators, the EPC800 for double-acting actuators, and the EPB800 specifically for the KOSO 5200LA actuator. This positioner utilizes a force-balance principle with a pilot valve that is a non-bleeding type, meaning it consumes air only when the valve is moving, which results in significantly lower steady-state air consumption compared to traditional bleeding-type positioners. The pilot valve design is common for both single-acting and double-acting types, and conversion between the two is possible. The input signal can be configured for split-range operation through span and zero adjustments, supporting 4-12 mA and 12-20 mA ranges in addition to the standard 4-20 mA signal. The EP800 can be used with both spring-return and double-acting actuators, and by adjusting the built-in capacity control spring, the positioner can be matched to low- or high-capacity actuators.

The housing is designed for demanding industrial environments and is available in weatherproof, explosion-proof, and intrinsically safe explosion-proof versions. The supply air pressure range is 140 to 700 kPa (or 140 to 800 kPa depending on the model), and the air consumption at 50% output pressure is 5 Nl/min for single-acting types at 140 kPa supply and 15 Nl/min for double-acting types at 400 kPa supply. The maximum capacity when the output side is vented to atmosphere is 175 Nl/min for single-acting types at 140 kPa supply and 400 Nl/min for double-acting types at 400 kPa supply. Performance specifications include linearity of ±1.0% for single-acting types and ±1.5% for double-acting types, with hysteresis of 0.5% and 0.8% respectively. Response level and repeatability are 0.1% and 0.2% for single-acting types, and 0.2% and 0.3% for double-acting types. The positioner is available with standard ambient temperature range of -20 to +80°C, a low-temperature version covering -50 to +60°C, and a high-temperature version for 0 to +100°C. Air and electrical connections are Rc 1/4 and G1/2 respectively. Typical industries include power generation, petrochemical, chemical processing, and general industrial automation. The combination of low air consumption, flexible configuration, and robust construction makes the EP800 a dependable choice for valve automation and process control efficiency.

Technical Specifications

Application Industry

1. Power generation

2. Petrochemical processing

3. Chemical processing

4. General industrial automation

5. Water and wastewater treatment

6. Pulp and paper mills

7. Food and beverage production

8. Pharmaceutical manufacturing

These industries require accurate valve positioning, reliable operation in demanding environments, and efficient air consumption to maintain process efficiency and safety. The EP800 is particularly suited for applications where low steady-state air consumption is important for energy savings, and where flexible configuration for single-acting or double-acting actuators is needed. Its non-bleeding pilot valve design ensures air is consumed only during valve movement, reducing operating costs. The positioner can be used with both KOSO and third-party pneumatic actuators that comply with standard mounting interfaces. With its broad temperature range options and explosion-proof certifications, the EP800 can be deployed in hazardous areas as well as ordinary plant locations.

Common Problems

1. Positioner does not respond to input signal – check the 4-20 mA loop for continuity, verify that the input impedance is 250 Ω ±5%, and confirm that supply air pressure is between 140 and 700 kPa; inspect the constant throttling orifice for blockage.

2. Valve does not stroke with setpoint change – verify pneumatic connections and supply pressure; confirm that the correct input signal is reaching the instrument and that the pilot valve is not stuck.

3. Output pressure changes slowly during downward stroke – inspect the amplifier diaphragm in the positioner for damage or wear; replace if necessary.

4. Poor linearity – check the magnet assembly for loose or unsoldered connections; verify that the feedback linkage is properly connected and adjusted.

5. Air leaks or pressure droop – inspect air supply connections, pilot valve, and actuator tubing for leaks; verify supply air quality and that the non-bleeding pilot valve is functioning correctly.

6. Positioner oscillates or hunts – adjust the capacity control spring setting, verify that the feedback linkage is secure, and confirm that the actuator is not oversized for the application.

7. Constant air consumption higher than expected – verify that the pilot valve is in the non-bleeding mode and not stuck in a bleeding position; check for internal air leaks.

8. Split-range operation not working – verify that the span and zero adjustments have been correctly configured for the 4-12 mA or 12-20 mA range.

9. Moisture ingress into enclosure – inspect cover seals, cable glands, and terminal box; verify weatherproof or explosion-proof integrity.

10. Erratic operation in high-vibration environments – verify that the positioner is securely mounted with all fasteners tightened, and check for loose feedback linkage connections.

Replacement Models

1. KOSO PP800 Pneumatic-Pneumatic Positioner (same platform, pneumatic signal input)

2. KOSO EP800 Series – EPA801, EPB801, EPC801

3. KOSO EP800 Series – EPA811, EPB811, EPC811

4. KOSO EP800 Series – EPA821, EPB821, EPC821

5. KOSO EP800 Series – EPA824

6. Fisher DVC2000

7. Fisher DVC6200

8. Samson 3730-3

9. Masoneilan SVI II AP

10. Flowserve Logix 520MD

Selection note: verify mounting flange compatibility, actuator type (single-acting or double-acting), stroke range, input signal type, supply pressure, and enclosure protection before substituting models. The EP800 is designed for pneumatic actuator-operated control valves and can be used with both KOSO and third-party actuators. For digital communication and advanced diagnostics, consider upgrading to the KOSO KGP5000 smart valve positioner.