What isolating valve to use in water systems is almost like asking “what shall I eat today ?” The choice is quite endless! In order to provide some meaningful answers in a short discussion – let’s discard some criteria where specialised valves might be required and deal with common water pipelines with size limitation of say 500mm and pressure ratings up to 40bar. So let’s discuss the most common valves for these applications and point out their merits and disadvantages.
The RSV (Resilient Gate valve) has become the most popular gate valve for the following reasons:
- Through Port design without “grooves” where particles can get trapped to prevent proper operation.
- Rubber coating of the gate ensures tight shutoff without heavy interference between seal and seat required – tehreby reducing torque requirements.
- Much less machining than traditional Wedge gate valevs resulting in less overall costs.
- Much better corrosion protection as there are no metal interferences between surfaces which destroy coatings.
- For all the above and other reasons, the RSV gate valve has become so popular that large volumes are being manufactured worldwide and the competition between companies has resulted in very low prices compared to Wedge gate valves.
The Butterfly valve has been around for many years and like most designs have evolved into better designs and qualities over a long period. They have gained tremendously in popularity for the following reasons:
- Cheaper to manufacture than gate valves
- More compact
- Easier to operate
Although at first Butterfly valves were limited in pressure rating to 16bar, with the advent of Metal Seated Butterfly valves they have evolved to 250bar ratings whilst still providing tight shutoff !! Probebly the biggest single factor against Butterfly valves is the fact that the disc is always in the flow path which causes a higher pressure drop than a gate valve and also increases the wear on the disc.
All the above factors should be looked at carefully when selecting isolating valves and represent just some of the criteria to consider in total valve selection for any pipeline system