Valves for gases

The safety relief valve is used for liquid and gas service. Safety relief valves function as relief valves for liquids and as safety valves for gases. 

Discharge coefficient of a safety valve for gases/vapors Pressure gradient of the real gas factor... 

DP Speed Factor. Pumping-speed efficiency depends on trap, valve, and system design. For gases having velocities close to the molecular velocity of the DP top jet, system-area utilization factors of 0.24 are the maximum that can be anticipated eg, less than one quarter of the molecules entering the system can be pumped away where the entrance area is the same as the cross-sectional area above the top jet (see Fig. 4). The system speed factor can be quoted together with the rate of contamination from the pump set. Utilization factors of <0.1 for N2 are common. 

For gases with specific heat ratios of approximately 1.4, the critical pressure ratio is approximately 0.5. For hydrocarbon service, this means that if the back-pressure on the relief valve is greater than 50% of the set pressure, then the capacity of the valve will be reduced. In other words, if the pressure in the relief piping at the valve outlet is greater than half (he set pressure, then a larger relief valve will be required to handle the same amount of fluid. 

Safely Valve normally used for steam service, but suitable for gases or vapors. When used in steam generation and process steam service the valves conform to the ASME Power Boikr Code as well as the ASME Pressure Vessel... 

Sizing for Gases or Vapors or Liquids for Conventional Valves with Constant Backpressure Only... 

The compressor manufacturer can control items a-c, e, f, and h however, the control of clearance volume at high compression ratios for gases/vapors with low specific heat ratios is of great concern. Compression efficiency is controlled by the clearance volume, valves, and valve pocket design. A decrease in compression efficiency leads to increased power requirements. ... 

Globe valves are used for gases, for control and wherever tight shutoff is required. Gate valves are for most other services. 

At the end of each work day, one person in the laboratory should have the responsibility for turning off the main cylinder valves for all gases. 

This equation defines the flow coefficient, Cv. Here, SG is the fluid specific gravity (relative to water), pw is the density of water, and hv is the head loss across the valve. The last form of Eq. (10-29) applies only for units of Q in gpm and hv in ft. Although Eq. (10-29) is similar to the flow equation for flow meters, the flow coefficient Cv is not dimensionless, as are the flow meter discharge coefficient and the loss coefficient (Af), but has dimensions of [L3][L/M]1/2. The value of Cv is thus different for each valve and also varies with the valve opening (or stem travel) for a given valve. Values for the valve Cv are determined by the manufacturer from measurements on each valve type. Because they are not dimensionless, the values will depend upon the specific units used for the quantities in Eq. (10-29). More specifically, the normal engineering (inconsistent) units of Cv are gpm/ (psi)1/2. [If the fluid density were included in Eq. (10-29) instead of SG, the dimensions of Cv would be L2, which follows from the inclusion of the effective valve flow area in the definition of Cv]. The reference fluid for the density is water for liquids and air for gases. 

The flow coefficient Cv is determined by calibration with water, and it is not entirely satisfactory for predicting the flow rate of compressible fluids under choked flow conditions. This has to do with the fact that different valves exhibit different pressure recovery characteristics with gases and hence will choke at different pressure ratios, which does not apply to liquids. For this reason, another flow coefficient, Cg, is often used for gases. Cg is determined by calibration with air under critical flow conditions (Fisher Controls, 1977). The corresponding flow equation for gas flow is... 

Lantern rings for pumps, bellow-type seals for centrifugal pumps hydraulic, pneumatic, earthmoving equipment cylinder valves for O2, CO2, refined gases, chlorine, ammonia... 

Schematic cross section of a burner, to be introduced into the reaction cell. A Threaded screw. B Cone to fit into the reaction cell opening. C Injector nozzle with two concentric tubes. D Twin valve for the inlet of two gases...

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