Valve high-pressure float

On a single-evaporator flooded system, a float valve can be fitted which will pass any drained liquid from the condenser direct to the evaporator. The action is the same as that of a steam trap. The float chamber is at condenser pressure and the control is termed a high-pressure float (Figure 8.3). 

High-pressure float valves plus handset throttle valves for some flooded and low-pressure receiver circuits. 

Standard high-vacuum techniques8-7 are used since some of the reagents and products are volatile, pyrophoric, and/or toxic. Since F2PI and F2PBr attack mercury, a mercury float-valve system cannot be used, and manometers should be protected with stopcocks until pressure measurements are to be made. ... 

Since some of the reagents and products have both a relatively high vapor pressure and a high toxicity, a standard high-vacuum system is recommended for carrying out the reactions and separating the products. Because some of the reactants and products attack mercury on long exposure, it is desirable to avoid mercury float valves and to protect manometers with stopcocks until pressure measurements are to be made. Essentially the same basic procedure is used for the preparation of chloro-, bromo-, and iododifluorophosphine. 

Simple flow controllers use the differential pressure at an adjustable restrictor the plus and minus sides are on the two sides of a spring-supported diaphragm. These controllers are used as backflow (check) valves or as isolation valves, which shut off if the flow is reversed or too high. Level controllers with floats are in condensate separators often coupled with simple temperature controllers as in Figure 12.28. These devices contain an electrical jump switch and operate therefore as two-point On-Off controllers. Controllers without auxiliary energy are used, where it is not essential to have high control accuracy and when one must do without the auxiliary power for safety reasons. 

Since, in most cases, columns with floating pressure have a higher pressure at high throughput and lower pressure at lower throughput, letdown valves will have highest APp at high flows and lowest APp at low flows. The prcxluct will usually be hot, so anticavitation trim may be required. 

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