Wedge gate valves (a.k.a gate valves) have a metal wedge which is forced against metal seats in the valve body to create a seal.
These valves are robust and usually have a long service life. But, they suffer some disadvantages:-
- The valve is often over-tightened to ensure a good seal. This makes it difficult to reopen. If leverage poles are used to apply extra force the valve can be damaged.
- The groove in the bottom of the body traps dirt and can stop the valve from closing properly.
- Anti-corrosion coatings near the valve seats are prone to damage, leading to corrosion of the valve body.
The resilient seated gate valve (RSV) was designed to overcome these problems. The gate has a rubber coating which makes for a better seal without needing excessive force or a body seat.
Early RSVs weren’t as good as those available today. Manufacturing quality was poor and the rubber lining sometimes detached from the gates. Today the rubber lining is moulded to the gate at high temperature and pressure leading to an excellent long-term bond. Some manufacturers now offer replacement guarantees of up to 20 years.
The strong bond between the gate and rubber makes the RSV a good choice in scour applications where high velocities might have torn the rubber in the past.
The manufacturing process, and economies of scale, have made these valves both cheaper and more readily avaiable than wedge gate valves. Fusion Bonded Epoxy (FBE) coating applied to the body and bonnet resist corrosion.
Other benefits include:-
- Better sealing performance.
- Lower opening and closing torque.
- Resilience to particles in the water. There is no groove at the bottom of the valve to trap dirt.
- Reduction in water hammer due to the rubber absorbing some of the impact of a pressure spike.
