Valve losses

White, K. H., Prediction and Measurement of Compressor Valve Loss, ASME 72-PET-4, New York, NY American Society of Mechanical Engi neers, 1972. 

Vacuum breaker, 291 Vacuum pump, 9 Vacuum service, 10 ejectors in, 11 liquid pi.ston, 9 liquid piston, 130 sliding vane, 10 Valve design, 62 Valve loss, reciprocating, 62 Valve unloader, 81 Valve velocity, 62 Valves... 

Control valve loss will be by difference, trying to maintain minimum 60% of pipe friction loss as minimum drop through valve, but usually not less than 10 psi. 

Note that this control valve loss exceeds 60 percent of this system loss, since the valve must take the difference. For other systems where this is not the situation, the system loss must be so adjusted as to assign a value (see earlier section on control valves) of approximately 10 to 20 psi or 25 to 60 percent of the system other than friction losses through the valve. For very low pressure systems, this minimum value of control valve drop may be lowered at the sacrifice of sensitive control. 

Friction, entrance and exit heads, valve losses... 

Bauer has studied losses in compressor cylinder performance associated with valve losses as they relate to overall efficiency. Bunn examines poppet valves for retrofitting cylinders. 

Condition 1 Figure 12-12. Start of the compression stroke. The cylinder is full of gas at suction pressure and essentially suction temperature (neglecting valve loss). The piston moves during compression toward condition (2) with suction and discharge valves closed. 

The slip S is the fraction of suction capacity loss. It consists of the volumetric efficiency loss fraction 1, the stuffing box loss fraction 1, and the valve loss fraction 1. The slip S is... 

The valve loss 1 is the loss due to the flow of fluid back through the valve during closing. This is of the order of 0.02 to 0.10 depending on the valve design. 

Figure 32.33 Some typical valve loss characteristics ...

Bernoulli s equation applied across the valve relates the pressure drop and flow rate in terms of the valve loss coefficient. This equation can be rearranged to give the flow rate as follows ... 

In the selection of the right valve, it is always best to work in conjunction with one of the manufacturer s personnel or a consultant who is familiar with the different types of valve available on the market and who can advise the best solution for the application. Different types of valve are available for a reason. These reasons might sometimes be exclusively based on low cost, but also many times solve a particular application problem. Savings at the expense of safety is not a good idea and ultimately leads to increased LCC (life cycle cost of the valve), loss of valuable product, environmental pollution, damage to installations and, most importandy, potential loss of life. 

The control systems enabled in the simulation were i) the IHX flow balance controller, which acts through primary compressor speed to maintain equal flow rate on the hot and cold sides of the IHX ii) the bypass flow controller which acts through bypass valve loss coefficient to maintain a shaft speed set point. Additionally the pre-cooler and intercooler cold side flow rates are supplied as forcing functions. The flow rates were roughly matched to decay heat level. The PCU shaft set point is decreased from 60 Hz over time to have the shaft speed more or less track the decreasing reactor energy production rate. 

The performance of reciprocating (piston) compressors with large valve area, or where valve losses are evaluated, is considered as close to... 

One cost-effective means of reducing compression valve losses and enhancing compressor efficiency is to replace valve plates with thermoplastic plates equipped with additional flow ports (i.e., openings in the plates for gas passage). Modifying valve plates in this manner will reduce horsepower valve losses due to the frictional pressure drop. 

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Valve loss reduction, 468- 471 rod loading, 469 gas engine drives, 469-471... 

For example, for one machine equipped with plastic poppet valves (i.e., compressor cylinder valves designed for high capacity but low compression ratios), valve losses as measured by a Beta Scan were reduced from 25% to 10% when the compression ratio was reduced from 1.42 to 1.28. This occurred even though the gas volume moved through the compressor increase by 50%. 

Description of the hazard or hazardous failure mode (so-called dangerous failure or failures) (e.g., failure to move valve, loss of heating, overpressure, etc.). 

In practice it is found that NPSHr for reciprocating pumps increases with the square of the volumetric flow rate. This is because check valve losses are of this form [18]. 

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