Samson Type 3755 Pneumatic Volume Booster, KVS 2.5

Type 3755 pneumatic volume booster for faster actuator response

The Samson Type 3755 is a pneumatic volume booster, also called an air capacity amplifier. It sits between a positioner and a pneumatic actuator and supplies the actuator with an air flow whose pressure equals the positioner signal pressure, but with a much larger volume. Seven Star LLC supplies the Type 3755 in Oman and the GCC as an independent supplier based in Muscat.

Large diaphragm and piston actuators fill and empty slowly through the small outputs of a typical positioner. The 3755 solves this: with KVS 2.5 m³/h for both supply and exhaust, a 1:1 signal-to-output ratio and low hysteresis, it speeds up stroking without changing the control signal. It is intended for actuators with an effective area of 1000 cm² or more, or a travel volume of 6 litres or more.

Decoding the Type 3755 article code

The 3755 article code defines the body, exhaust and thread through a set of single digits. The options that the data sheet prints are:

Type 3755 technical specifications

How the 3755 boosts air flow

When the positioner raises its signal, pressure above the diaphragm rises, and the pressure difference opens the supply plug. Supply air up to 10 bar then flows to the actuator until the pressure under the diaphragm balances the signal. When the positioner lowers the signal, the exhaust plug opens and the actuator is vented through the exhaust port. A balanced plug keeps the reversing pressure constant, and the filter disk gives low noise on the -1 version.

The bypass restriction screw lets a small amount of air pass directly and tunes the booster to the loop. It has a linear characteristic and a lock nut. Its setting is part of loop tuning and should be adjusted while watching the step response of the actual valve.

Where the 3755 fits next to positioners and lock-up valves

The booster is mounted in the signal line between the positioner output and the actuator, with air flowing from the supply port to the actuator port as the arrow on the body shows. In loops that also use a Type 3709 lock-up valve for fail-in-place behaviour, the Samson application drawings place the volume booster upstream of the lock-up valve. The booster works together with the positioner of the valve, so the positioner output pressure must lie within the signal limits of the booster.

Selection checklist for the Type 3755

• Actuator size: effective area of at least 1000 cm² or travel volume of at least 6 litres.
• Body material: aluminum or stainless steel; the stainless version is rated for IP66 and has a higher weight.
• Exhaust: sintered filter disk for silent venting, or a threaded exhaust piped away.
• Thread standard: G or NPT, to match instrument-air tubing.
• Temperature: standard version to –40 °C or low-temperature version to –55 °C.
• Pressure: actuator and signal lines are limited to 7 bar, supply to 10 bar.
• Safety use: aluminum body, standard temperature, and review the safety manual SH 8393 first.

Installation, commissioning and maintenance of the 3755

Mount the unit close to the actuator. For the IP44 rating of the aluminum body, the exhaust side must face downward or sideways. Use clean, dry air meeting ISO 8573-1 classes, because the plug seals and filter disk are sensitive to oil and particles. After installation, set the bypass restriction while observing the step response, then lock and lead-seal it. Periodically inspect the filter disk for clogging or corrosion deposits and replace diaphragm and seals during shutdowns if the control becomes sluggish or leaks to atmosphere.

Typical 3755 applications in Oman and the GCC

Volume boosters are used on large control valves and dampers where stroking time matters: anti-surge and compressor recycle valves, large butterfly valves in cooling water and seawater lines, boiler and turbine bypass valves, and large diaphragm actuators in power stations, desalination and gas plants. In hot, dusty coastal conditions in Oman, the stainless steel body with threaded exhaust piped to a clean area limits ingress and corrosion, while the aluminum version is the lighter option for sheltered locations.

Information to send with an RFQ for the 3755

• Full 3755 article code or the options from the table
• Actuator make, type, effective area or volume and stroking time target
• Positioner type and supply pressure
• Thread type and exhaust arrangement
• Ambient temperature range
• Quantity

Documents and quotation

The Samson datasheet for the Type 3755 is attached on this page. Send the 3755 code and actuator information to Seven Star LLC for a quotation in Oman and the GCC.