Masoneilan 172-50 Differential Pressure Regulator, Single and Double Diaphragm

Overview

The Masoneilan 172-50 is the differential pressure version of the 172 Series direct-operated regulator from Baker Hughes. In the Masoneilan numbering system the option code 50 means differential action, so a 172-50 does not hold a gauge pressure at a fixed value; it holds the difference between two controlled pressures at an adjustable set point. The instruction manual describes two construction groups, a single diaphragm design and a double diaphragm design with a vented chamber between the diaphragms, and both are built on the compact body and trim used across the 171-172 family, in sizes from 1/2 inch to 2 inch (DN15 to DN50).

In Oman and the GCC, Seven Star LLC supplies the Masoneilan 172-50 to process plants, packaged-system builders and EPC contractors in the Sultanate of Oman and across the GCC. Our instrumentation division in Muscat helps engineers decide between the single and double diaphragm groups, confirm body material, trim and spring range, and obtain the Baker Hughes technical specification and instruction manual for the exact unit.

Differential Operating Principle of the Masoneilan 172-50

In a Masoneilan 172-50 regulator one controlled pressure acts under the diaphragm through the internal sensing path in the body, while the other is piped to the sensing connection on the spring housing and acts over the diaphragm. The adjustable spring holds the plug open. When the differential grows beyond the set point, the extra force on the diaphragm compresses the spring and closes the plug, and when the differential falls the spring reopens it. The result is a regulator that keeps one pressure above a reference pressure by a fixed amount, which is the usual way to control a seal gas, a barrier fluid or a lube supply with the Masoneilan 172-50.

The two groups differ in how the diaphragm is arranged. Group 1 has one diaphragm: one pressure acts under it through the internal sensing connection and the other acts over it through the line on the spring housing. Group 2 has two diaphragms separated by a chamber that communicates with the outside. The controlled pressures act under the lower diaphragm and over the upper diaphragm, and if either diaphragm leaks, the fluid escapes into the vented chamber rather than into the other process line.

Engineering Design of the Masoneilan 172-50

The Masoneilan 172-50 uses the 172 high-pressure insert, plug and disc construction, with a 316 stainless steel seat and plug stem and an elastomer or metal disc. Bodies are offered in carbon steel and 316 stainless steel, with full carbon steel and full 316 stainless steel constructions for wider temperature limits and special materials such as LCB, NACE WCC, 316L, 317, duplex, super duplex, Monel and Hastelloy B or C on request. Actuator sizes 220 and 360 in carbon or stainless steel use a multi-part spring case, and an optional handwheel is available.

For the double diaphragm group the actuator carries an actuator ring and an intermediate plate between the two diaphragms, and the chamber between them must be piped to a safe place that is constantly at atmospheric pressure. The manual allows that connection to be closed with a plug or with a pressure gauge fitted with an electrical contact, so a diaphragm failure can be signalled remotely, provided that the downstream piping is protected by a safety valve.

Key Features

The following points explain why the Masoneilan 172-50 is specified where a differential, rather than an absolute, pressure must be maintained:

• Differential action on the Masoneilan 172-50 holds one pressure above a reference pressure by an adjustable amount, with no air supply or electronic loop.
• The single diaphragm group of the Masoneilan 172-50 gives the simplest construction for clean, compatible fluids on both sensing lines.
• A double diaphragm group isolates the two process fluids with a vented chamber and allows remote signalling of diaphragm failure.
• The adjusting screw sets the differential directly, turning clockwise to raise it and counter-clockwise to lower it.
• Threaded and flanged bodies from DN15 to DN50 allow replacement of existing units and custom face-to-face lengths on request.
• Diaphragm, disc and body materials can be chosen for service from -196°C to 455°C depending on construction.
• In-line diaphragm replacement is possible where the regulator can be isolated and fully vented.
• An external 1/8 inch sensing connection is available for points where pressure variations at the consumer must be avoided.

Industrial Applications

The Masoneilan 172-50 is typically applied to seal-gas and seal-oil systems, barrier-fluid pots on rotating equipment, purge and blanketing lines that must stay above a vessel pressure, and lubrication circuits where the oil must reach the bearing at a fixed margin above the casing pressure. In Oman these duties arise on compressor and pump trains at gas processing and refinery sites, on desalination and power plants along the Batinah coast, and on manufacturing lines in the Sohar and Salalah free zones.

In Oman and the GCC, Seven Star LLC distributes the Masoneilan 172-50 alongside the standard Masoneilan 172 Series pressure reducing regulator and the lower pressure Masoneilan 174 Series regulator. For every Masoneilan 172-50 the Baker Hughes installation diagrams call for isolation valves upstream, downstream and on each sensing and discharge line, and a gauge on the sensing line so the differential can be watched during calibration. We can supply the regulator with that accessory set.

Technical Specifications

The table below summarises the Masoneilan 172-50 datasheet values, drawn from the Baker Hughes technical specification and instruction manual for the 171-172 family. The datasheet covers the full tables of Cv, set ranges and allowable pressure drop.

Standard spring ranges in the 172 specification run from 1.36 to 667 psig (0.094 to 46 barg) over actuator sizes 220, 140, 130, 120 and 100, with maximum outlet pressure of 42, 145, 362, 470 and 754 psig respectively. The usable differential span of a given 172-50 is fixed at the factory, so please confirm the spring range for your differential with our team.

Related Masoneilan regulators include the Masoneilan 535V Series microflow regulator.

Request a Quote for Masoneilan 172-50

To request pricing or technical support for the Masoneilan 172-50, send a formal RFQ to the Seven Star LLC instrumentation division stating the two controlled pressures, the required differential, the fluid, the flow rate and the body size and end connection. We confirm the single or double diaphragm group, advise on regional warehouse availability and provide the Baker Hughes technical datasheet and instruction manual for download from this page. In Oman and the GCC, Seven Star LLC delivers genuine regulators with manufacturer documentation and responsive local support.