Alloy 20 Dual Plate Lug Type Check Valve Manufacturer and Supplier in Africa

Acid transfer lines often need a non-return valve that closes quickly without occupying the space required by a conventional swing check valve. An Alloy 20 dual plate lug type check valve addresses this requirement through two lightweight closing plates, spring-assisted movement and a compact lugged body. Alloy 20 is particularly useful where sulphuric acid or chloride contamination makes ordinary stainless steel unsuitable. African Valve is a leading Alloy 20 Dual Plate Lug Type Check Valve Manufacturer and Supplier in Africa, supplying projects in Nigeria, Egypt, South Africa, Kenya and Ghana, with export support for the Middle East, Europe and other international markets.

What Happens Inside the Valve During Pump Shutdown?

Two semicircular plates are mounted around a central hinge pin. During normal flow, fluid pressure pushes both plates open against the spring force. As the pump slows or stops, the torsion springs start returning the plates before reverse velocity becomes severe.This matters because the closing distance is shorter than the travel of a single swing disc. The lighter plates also carry less inertia. In correctly sized systems, these characteristics reduce the impact associated with valve slam and help limit pressure surges in the pipeline.Spring torque should match the service. A spring that is unnecessarily strong can increase opening pressure, while insufficient spring force may allow delayed closure.

Why Use a Lugged Body?

Threaded lugs are cast or machined around the valve circumference. Bolts enter from each flange side instead of passing completely through the assembly. This arrangement keeps the valve centred and allows each pipe flange to be fastened separately.

Lug construction is useful where pipeline sections may need to be disconnected during maintenance. However, suitability for dead-end operation must be confirmed from the valve design and pressure rating. Not every lug valve is rated to hold full pressure with one flange removed.

Alloy 20 in Acidic Service

Cast pressure-retaining parts are commonly specified in ASTM A351 CN7M. Forged internal parts may be produced from ASTM A182 F20. Nickel, chromium, molybdenum and copper provide Alloy 20 with useful resistance to sulphuric acid and several mixed chemical environments.

The complete trim must be reviewed, not only the body. Hinge pins, springs, plates and fasteners remain exposed to the fluid and therefore need compatible metallurgy. Depending on temperature and leakage requirements, seats may be PTFE, reinforced PTFE or metal.

Soft seats can provide low leakage in clean chemical service. Metal seating is more appropriate where temperature, suspended particles or erosion could damage a polymer seat.

Technical Specifications

Size Range: DN50 to DN1200
Pressure Ratings: Class 150 to Class 600; PN10 to PN100
Design Standards: API 594 and ASME B16.34
Testing Standard: API 598
End Connections: Lug type suitable for ASME B16.5 or EN flanges
Operation: Automatic spring-assisted closure

Engineering Features

• Short closing travel reduces the time available for reverse flow to develop.

• Separate plates carry less rotating mass than a full swing disc.

• Threaded lugs maintain alignment between the mating flanges.

• Alloy 20 construction supports sulphuric acid and chloride-bearing duties.

• Spring, plate and seat materials can be selected for the actual fluid.

• The compact body reduces installation length and pipeline weight.

Where Is This Valve Normally Installed?

Typical installations include sulphuric acid transfer lines, fertilizer units, chemical dosing packages, acid recovery systems, pickling plants and corrosive water-treatment piping. It is also used on pump discharge lines where a faster response is needed than a traditional swing check valve can provide.

Inspection Before Dispatch

The lug threads, body dimensions, plate movement and hinge alignment are checked before pressure testing. Hydrostatic shell testing confirms body integrity, while seat testing identifies leakage in the closed position. Positive Material Identification may be carried out on Alloy 20 components when required by the inspection plan. Material Test Certificates, pressure-test reports and dimensional records can be supplied for EPC documentation.