FAQ - Valves and Fittings

The range includes metering valves, needle valves, packless valves, check valves, bleed valves, ball valves, trunnion valves, selector valves, high-pressure valves and application-specific instrumentation valves. View Valves on the Gommer website.

Both use a tapered stem, but a metering valve is optimised for precise and repeatable flow adjustment. A needle valve can provide throttling but is more commonly selected for isolation and general flow adjustment.

A ball valve is ideal for quick quarter-turn isolation and usually produces relatively low pressure drop when fully open. A needle valve is more suitable when gradual flow adjustment is required.

Packless valves use a diaphragm or bellows arrangement instead of conventional stem packing to isolate the process from the atmosphere. They are particularly attractive for toxic, high-purity, vacuum and speciality-gas applications.

A check valve allows flow in one direction and automatically restricts reverse flow. It is used to prevent backflow, cross contamination or reverse pressurisation. View Check Valves on the Gommer website.

Cracking pressure is the differential pressure at which a check valve begins to open. Low cracking pressures minimise resistance to forward flow, while higher cracking pressures can help prevent unwanted opening caused by minor pressure fluctuations.

A bleed valve provides a controlled means of venting trapped pressure or draining a small volume. It is frequently combined with an isolation valve in block-and-bleed arrangements.

A trunnion-supported ball is mechanically supported rather than relying solely on the seats. This arrangement can reduce seat loading and operating torque at high differential pressures.

A selector valve allows an operator to route one of several streams to a common outlet or one inlet to selected outlets. Applications include analyser systems, calibration panels and sample switching.

A monoflange combines process isolation, bleed and sometimes secondary isolation functions in a compact flange-mounted body, reducing separate threaded components and potential leak paths.

A block-and-bleed arrangement isolates process pressure and allows the trapped downstream volume to be safely vented. Double-block-and-bleed configurations use two isolation barriers with a bleed point between them.

Cv represents flow capacity. Selection should consider required flow, medium, pressure drop and desired control behaviour. For metering applications, the relationship between stem position and Cv can be more important than maximum Cv alone.

Precision metering valves are generally the first choice where very small and repeatable flows must be adjusted manually. HOKE precision metering-valve families are examples intended for analytical and instrumentation service.

Gyrolok is HOKE's twin-ferrule tube-fitting system. The design uses a front ferrule to create the seal and a rear ferrule to provide controlled tube grip. View Gyrolok on the Gommer website.

As the nut is tightened, the ferrules move axially and radially around the tube. Correct installation creates a pressure-tight seal while mechanically gripping the tube.

Correctly installed tube fittings can generally be disconnected and remade within manufacturer guidelines. The fitting body and ferrules should be inspected and the manufacturer's remake procedure followed.

It is best practice to use nuts, ferrules and bodies as a complete system from one manufacturer. Components can differ in geometry, material condition and assembly behaviour even when they appear similar.

No. A 12 mm tube and a 1/2-inch tube are not the same outside diameter. Tube and fitting dimensions must match exactly.

A bulkhead fitting passes a tube connection through a panel or enclosure wall and is mechanically secured to that panel. Typical applications include analyser cabinets and sampling panels.

A port connector directly joins compatible tube-fitting ports without the need for a separate piece of tubing, reducing assembly length and the number of components.

A tube adapter presents a tube-like end that can be inserted into a tube fitting while providing another connection type on its opposite end.

Weld fittings provide permanent high-integrity connections where mechanical tube fittings are not desired or where project specifications require welding.

NPT and BSPT are tapered thread systems. BSPP is parallel and normally requires a separate sealing feature such as an O-ring, bonded seal or gasket. The threads are not automatically interchangeable.

A G thread is a parallel pipe thread defined by ISO 228. Because the thread itself is not intended to provide the pressure seal, the design normally incorporates a separate sealing surface.

Depending on product range, materials can include 316/316L stainless steel, brass, Monel, Hastelloy, Inconel, Incoloy, Duplex, Super Duplex, PTFE and PFA.

Hastelloy alloys can provide significantly better resistance than standard stainless steel to certain acids, chlorides and highly corrosive chemical environments. Selection depends on exact chemical composition, concentration and temperature.

Monel nickel-copper alloys are used in selected corrosive services and can provide strong resistance in specific marine, chemical and hydrofluoric-acid environments.

These nickel-based alloys are commonly associated with demanding temperature and corrosion conditions. The optimum alloy depends on temperature, oxidation, chemical exposure and mechanical requirements.

Selected products can be supplied in materials and hardness conditions suitable for sour-service requirements. Where NACE MR0175 / ISO 15156 applies, the complete material specification and environmental limits must be considered.

Suitable components can be supplied cleaned and prepared for oxygen service. This must be specified when ordering because cleanliness is part of the product requirement.

Yes, many instrumentation components are used in hydrogen systems. Pressure, material condition, valve design, connection integrity and leak-tightness need to be evaluated.

Pressure capability varies by product family, size, material and temperature. HIP products extend into very-high-pressure applications. The allowable pressure of the complete assembly is governed by its lowest-rated component.

Yes. Assemblies can include valves, manifolds, tube fittings, tubing, regulators, gauges and filters and can be assembled, tagged and pressure tested before delivery. View Contact and Engineered Assemblies on the Gommer website.

Provide the medium, pressure, temperature, required flow, tubing dimensions and connection requirements. Our technical team can help select a suitable valve, fitting or complete assembly.