Flow Control, Flow Control April 2019

upstream seat because the downstream seat is forced by the ball into the internal valve body where sealing occurs on the back side of the downstream seat Radial grooves do not make the valve unidirectional The valve remains bidirectional because both seats are identical the forces that occur inside the valve are also identical keeping the valve bidirectional Thermal fluid expansion In a floating ball valve the cavity created between the two seats is an absolute ideal Check Valves From drinking water Versatile acetal copolymer Rated up to 200 F 230 psi NBR EPDM or silicone seals Figure 6 Left To prevent cavity pressure increase place a vent hole pointing upstream when the valve is in the closed position This however makes the valve unidirectional Figure 7 Right Self relieving seats containment vessel for pressure increases Surprisingly there is a magnitude of pressure rise associated with temperature increases of a trapped incompressible due to thermal expansion Ordinary water trapped without any air will increase in pressure about 100 psi for every degree in Fahrenheit of temperature increase For example 10 F will raise the pressure approximately 1000 psi And the pressure temperature relationship of most common liquids is approximately 90 to 110 psi per degree Fahrenheit In fact ANSI B1634 Covering a range of sizes from 5 16 to 2 NEOPERL springloaded check valves are easy to insert into your application device and provide tight sealing 100 tested To hot water Glass filled Noryl Rated up to 250 F 230 psi EPDM seals NEOPERL Inc Waterbury CT Tel 203 756 8891 Fax 203 754 5868 info@ neoperl com www neoperl com Paragraph 233 Thermal Fluid Expansion states It is the responsibility of the user to provide or require to be provided means in design installation or operation procedure to assure that pressure in the valve will not exceed that allowed by this standard for the attained temperature There are a couple ways ball valve manufacturers address the problem of increased cavity pressure due to thermal fluid expansion While the valve is in the open position any pressure in the cavity created by the ball seats and body can easily be vented 24 April 2019 Flow Control