Stem Extension for Buried Service
A stem extension is a need when valves are being installed in underground pipeline making the valve operator non accessible.
RV valves offer a wide variety of stem extensions for manual operated valves as well as for actuated valves, including gas- over-oil operated valves.
The stem extension includes the complete system of grease injection, actuator gas supply, etc as a part of it.
The seat assembly, either soft seat or metal seat, which seals against the ball is provided with coil springs on its back side. The coil springs press the seat assembly against the ball making sure the contact between the seat area and the ball even in absence of line pressure.
When line pressure increases, the seat differential area (C=A-B) creates a piston effect forcing the seat against the ball. This additional load increases the effectiveness of the seat/ball interface.
The higher the line pressure is the greater the piston effect.
Automatic Cavity Pressure Relief
The pressure-actuated seat construction, used in trunnion ball valves ensures positive relief of excess of valve central cavity pressure. If valve central cavity pressure exceeds
a pre-set pressure in the seat, the seat assembly will automatically back-off to relieve the excess of pressure.
Double Piston Effect (optional)
With normal floating seats a ball valve is-bi-directional, creating a single seal on the seat exposed to line pressure. The opposing seat vents pressure downstream. If the upstream seat fails, it may be appropriate to use the downstream seat as a back up seal to the primary seat. Modified seats can offer this feature. The outer diameter of the seat is designed with a double piston profile, exposing more surface area to cavity pressure that a normal floating seat. In the case of an upstream leak, this enhances the contact pressure between downstream seat and ball.
The differential area A= B-C creates a piston effect forcing the seat against the ball.
In such cases, it is recommended that an automatic pressure relief valve be installed to protect the body cavity from excess pressure.
As an option, it is possible to adopt the double piston effect on one side only. Although this eliminates the need for a pressure relief valve, it does make the valve uni-directional.
Double Block-Bleed (optional)
Because the floating seats seal, both upstream and downstream, simultaneously, double block and bleed procedures can be performed. With the valve under pressure, the body cavity may be vented or drained to the atmosphere through the bleed valve.
Anti Blow-Out Stem
RV valves are always provided with anti-blow out stem design, which ensures total safety and integrity.
Fire Safe Design
RV valves are of FIRE SAFE design, which substantially prevent the leakage when valve is subject to high temperatures. In case of fire accident inside the valve, seals, and seat inserts (for soft seated valves) are melted and then a metal to metal seat is made between the metallic seat and the ball ensuring a degree internal sealing tightness. All o-ring are also disappeared and only graphite back-up rings remain in seats and valve stem, making the valve tight for leakages to the atmosphere.
RV valve designs conform requirements of API 6FA, API607 and BS6755.