- NOMINAL DIAMETER
The nominal diameter is indicated on the body of the valve in inches or by “DN” followed by the value is mm unit of measure, which corresponds to the size expressed in the inches, e.g.: DN20 is equivalent to ¾ inch NPT or BSP connection.
2. EFFECTIVE DIAMETER
The effective diameter indicates the actual port diameter in the ball. This equals the nominal diameter of the ball only in the case of a full-bore valve. In case the actual port diameter in the ball is one size smaller than the valve’s size, (e.g.: ¾” ball valve with ½” port in the ball) the valve is referred as “reduced-bore.” While in case the actual port diameter in the ball is in between the valve’s size and the one size smaller, (e.g.: ¾” ball valve with 5/8” port in the ball) the valve is referred as “standard-bore.”
3. FLOW COEFFICIENT
The CV value is an indication of the capacity of a valve and is often used to describe the performance of control valves. The CV coefficient is often used to describe the hydraulic characteristics of elements in a pipeline. The definition of CV is the number of U.S. gallons per minute (GPM) of 60 F water flowing through a valve results in a 1 pound per square inch (psi) pressure drop across the device.
It is essential that the limits set by the manufacturer are observed to achieve the best results from the valve. If are used higher temperatures and pressures, than recommended, the natural elasticity of the Teflon will be exceeded, and permanent deformation will result in leakage.
5. RESISTANCE TO CORROSION
The table of chemical compatibilities indicates the suitability of brass material and other materials for use with various fluids. However, the table is not designed to provide a complete answer to all applications. Please contact your Enolgas USA Inc. representative or directly Enolgas USA Inc. for clarifications.
6. PRACTICAL TESTS
In the circumstances involving unusual applications, it is often safer to carry out a practical test to determine the compatibility of the fluid to the brass and Teflon. Obviously, there are instances where theoretical information and experience are not available as a guide.
In ball valves, the loss of head is increased by the square of the reduction bore; this means that a small bore reduction will result in a large loss of head.
However, the situation is not improved by using a hollow ball. Head loss becomes greater due to turbulence within the ball. Tests show that in a hollow full-bore valve the loss head is 42% greater than a standard full-bore valve. A ¾” valve, (DN 20), hollow full bore ball is capable of passing less volume of fluid in one hour than a DN15 valve with regular full bore ball. (i.e., one size smaller has larger capacity).
The performances of ball valves are shown in the diagrams with the interaction between temperature and pressure. The horizontal line indicates the temperature and the vertical axis indicates the pressure in PSI/BAR (atmospheres). Each co-ordinate delimits the field of use of a given size of the valve.
8. CHOOSING A BALL VALVE
When selecting an item, it is essential that both quality and price factors are considered. If two products appear visually similar, there is a natural tendency to select the product with the lower price. However in the case of a ball valve the external appearance is not the most important aspect (assuming that the finish and thickness of materials are similar) in selecting the correct valve to give trouble-free long life. Therefore it is preferable to determine the level of quality and then compare the costs.