Rotork Fairchild Model 4000ABP Back Pressure Regulator

The Rotork Fairchild Model 4000ABP is a pneumatic precision back pressure regulator of the no-bleed type. Rotork describes it as controlling system back pressure precisely, and the large relief valve gives it a high exhaust capacity: the datasheet quotes 150 SCFM (255 m3/hr) at a 90 psig setpoint, far more than the 40 SCFM of the smaller Model 10BP. Sensitivity is 1/2 inch water column, and the unit is certified for Canadian registration (CRN) in all territories and provinces.

Force balance with a large relief valve

Upstream pressure travels through the aspirator tube to the underside of the diaphragm assembly. Turning the range screw compresses the range spring, which pushes down on the top of the assembly. While the pressure force is lower than the spring force, the relief valve stays shut. If system pressure climbs beyond the setpoint, the assembly lifts the relief valve from its seat and vents the surplus; when pressure drops, the valve closes. The aspirator tube compensates for upstream pressure build-up under flow, and a separate control chamber keeps the diaphragm out of the main flow so it does not hunt or buzz. Like the other units in the series it can be serviced without removing it from the line.

Technical specifications

Ordering choices

The catalog number starts with the series digits, then a range digit (2 for 0.5-10 psig, 3 for 0.5-30, 4 for 1-60, 6 for 2-150), a port size digit (3, 4 or 6) and letters for thread (N, H or U), elastomer (N nitrile or J fluorocarbon) and actuator (K knob or T tamperproof). A zinc plated mounting bracket kit, P/N 20555-1, is sold separately. Installation, operation and maintenance details are in Fairchild instruction IS-1004000ABP.

Selection notes

Pick the 4000ABP when the vent must pass a high flow, for example when relieving a large header or a process air volume that fills quickly. Pick the smaller 10BP when you need finer sensitivity (under 1/8 inch) and lower capacity. Confirm the setpoint, the maximum inlet pressure (250 psig), the port size and thread, the elastomer for the gas, and the flow that has to be vented. This is a control regulator; it does not replace a safety relief valve where one is required.

How the Fairchild Model 4000ABP works

A back pressure regulator holds the pressure upstream of itself, which is the opposite job of a normal reducing regulator. In the Fairchild Model 4000ABP, upstream pressure travels through the aspirator tube to the underside of the diaphragm assembly. The range spring pushes down on the top. While the pressure force stays below the spring force, the relief valve is shut and nothing is vented. When system pressure rises above the setpoint, the assembly lifts the relief valve off its seat and the surplus air leaves through the exhaust. When pressure falls back, the valve closes again. Because it is a no-bleed design, it does not waste air at rest.

Where the Fairchild Model 4000ABP is used

• Holding a steady pressure in an instrument air header
• Controlling pressure in a blanketing or purge line
• Relieving surplus pressure from a pneumatic process line
• Protecting equipment from pressure build-up in a closed system
• Test rigs and packaging machines that need a stable back pressure

Selection checklist for the Fairchild Model 4000ABP

• Setpoint range: 0.5 to 10, 0.5 to 30, 1 to 60 or 2 to 150 psig
• Maximum inlet pressure of 250 psig, which is 17 bar
• Port size: 3/8, 1/2 or 3/4 inch
• Thread: NPT, BSPP or BSPT
• Elastomer: nitrile, or fluorocarbon on the 2 to 150 psig range
• Exhaust flow needed, compared with 150 SCFM at 90 psig
• Ambient temperature from -40 to 200 degF
• Hazardous area classification of the site

Installation, commissioning and maintenance notes

Fit the regulator in the line so that the inlet sees the pressure to be held and the exhaust can vent safely. Keep the supply clean and dry, because dirt on the seat can hold the relief valve open. Turn the range screw slowly while watching a gauge, until the line pressure settles at the setpoint. Check the unit at planned stops for leaks and wear. The regulator can be serviced without removing it from the line, which shortens shutdowns.

Requesting a quotation for the Fairchild Model 4000ABP

Please send the setpoint range, the port size and thread, the elastomer and the quantity needed. Seven Star LLC serves industrial customers in Oman and the GCC and replies with a quotation based on the information provided.

Fairchild Model 4000ABP sensitivity

The sensitivity is 1/2 inch of water column, so the regulator reacts to very small pressure changes at the setpoint.

Fairchild Model 4000ABP materials

The body and housing are aluminum, the diaphragms and seals are nitrile, and the trim is zinc plated steel and brass.

Fairchild Model 4000ABP hazardous areas

The datasheet lists the regulator as acceptable for Zones 1 and 2 gas, Groups IIA and IIB, and Zones 21 and 22 dust.

Fairchild Model 4000ABP ordering code

The catalog number is built from the series digits, a range digit, a port size digit and letters for thread and elastomer, so state each choice clearly.

Pressure regulator records for Fairchild Model 4000ABP

Keep the setpoint, the date of the last check and the catalog number with the maintenance file.

Choosing the right Fairchild Model 4000ABP range

Pick the range so the working setpoint sits in the middle of the span, not at either end. This gives the finest adjustment and the longest spring life.

Documents and quotation

The Rotork datasheet is attached. Send Seven Star LLC the catalog number or the setpoint, port and thread requirement and we will quote from our regulators range. Pressure reducing alternatives include the Rotork Fairchild Model 1000.