Flowserve Durco G4 Sleeveline Non-Lubricated Plug Valve

Durco G4 Sleeveline non-lubricated plug valves for chemical service

The Flowserve Durco G4 Sleeveline is a non-lubricated, PTFE-sleeved plug valve designed for corrosive chemical services where drop-tight shut-off is essential. The tapered plug wedges into a PTFE sleeve that surrounds the plug ports and seals the circumference top and bottom, and a fluoropolymer reverse-lip diaphragm seals the stem. Seven Star LLC supplies Durco valves and spares in Oman and the GCC as an independent supplier in Muscat; this page describes the G4 family so that you can specify the right variant.

G4 is a family code. It is extended by the G4B Marathon for high-cycle duty, the TSG4 severe-service valve, the G4Z fire-sealed valve with the G4Z-HF alkylation version, and V-port control versions. Each valve is configured by size, class, body and plug material, sleeve, end connection and operator, so a complete model code is built from the datasheet “How to Specify” table.

G4 Sleeveline technical specifications

How the G4 sleeve and stem seal work

Line sealing comes from the compressive wedge fit of the tapered plug in the PTFE sleeve. The seal does not depend on line pressure, there is no metal-to-metal contact, and no lubricant is ever needed, so the valve stays free-turning throughout its life. The wiping action between sleeve and plug helps with slurry handling, and there are no cavities where product can accumulate.

When the sleeve wears, two adjuster fasteners drive the plug deeper into the sleeve. This adjustment is done in line and under pressure in seconds, and it is independent of the stem seal. In the stem area, the reverse-lip diaphragm is self-energising: line pressure pushes the lip against the stem for a dynamic seal, while an interference fit gives the static seal.

G4B, TSG4, G4Z and V-port variants

Where the G4 fits and related parts

The G4 family is typically found on acid, caustic, solvent, chlorine and other aggressive chemical lines, as well as on alkylation units and general chemical processing. In process lines it is often paired with Flowserve Automax, Norbro or Worcester actuators for automated on-off or modulating packages, since the torque is relatively constant and no lubrication is required. Related items include handwheel extensions, T-handle wrenches, chain wheels, double-end wrenches and gear operators, plus replacement sleeves, diaphragms, thrust collars and O-ring kits.

G4 selection and ordering checklist

• Valve size from 1/2 in upwards and pressure class (150 or 300), and the end connection: flanged ANSI or DIN, screwed, socket weld or butt weld.
• Process fluid, concentration, temperature and pressure, including whether vacuum or thermal cycling occurs.
• Variant: G4 standard, G4B Marathon for cycling, TSG4 for toxic or sub-zero, G4Z fire sealed, or a V-port control version.
• Body and plug material appropriate to the chemical, and sleeve and diaphragm material.
• Number of ways: straightaway (2-way) or 3-way, with port arrangement.
• Operator: wrench, gear, handwheel, chain wheel or actuator, and installation orientation.
• Options: chlorine service, NACE trim, oxygen cleaning, phosgene preparation, jacket, Kalrez O-rings, drilled and tapped flange, block and bleed.

The datasheet gives a sample model string, 4-G4B-31C810D1M33Z, described as a 4 in Durco G4 Marathon plug valve, ASME Class 300, two-way, carbon steel body, 316 stainless plug, CD4MCuN top cap, Durlon sleeve, B7 fasteners and fire sealed. Use this as a guide to the level of detail required in an enquiry.

Installation, commissioning and maintenance of the G4

Flush and clean the line before installing, as particles can score the sleeve. Check that the flanges are aligned and do not load the body, and check the stop collar and flow indication on three-way valves, where the port positions are marked A, B and C. After installation, cycle the valve and confirm that torque is smooth.

When a valve starts to weep at the lower end of its temperature range, or after thermal cycling, the in-line adjustment restores the seal without removing the valve. Sleeves, diaphragms and O-rings are the usual spare parts; the datasheet recommends reading the Flowserve selection, installation, operation and maintenance instruction before installing, operating or repairing any valve, and operators should be trained for the service.

Typical G4 applications in Oman and the GCC

In Oman and the GCC the Sleeveline family fits chemical and petrochemical plants, chlor-alkali and water treatment chemical dosing, refinery alkylation and acid services, fertiliser plants and desalination plants using chemical cleaning. Heat, dust and high humidity make stem-seal integrity and corrosion-resistant materials important choices.

Information to send with an RFQ for a G4 valve

Send the valve size, class and ends, the variant (G4, G4B, TSG4, G4Z), the process fluid with concentration, operating pressure and temperature, body, plug and sleeve materials, operator type, special options and quantity. For replacement parts give the nameplate details and a photograph of the valve.

Documents and quotation

This family is documented in a large Flowserve catalogue. Send us the part number or model code and we will confirm the available documents for your specific valve.

Seven Star LLC will prepare a quotation for Durco G4 valves or spares for delivery across Oman and the GCC.