Butterfly valves

Eig. 20. Cut view of Chlorine Engineers membrane bag cell a, manifold b, frame c, partition plate d, sealing plug e, recirculated NaOH inlet f, cathode g, anode h, cathode can i, membrane bag j, base k, butterfly valve 1, feed brine m, depleted brine n, caustic outlet. 

Sodium fluoride is normally manufactured by the reaction of hydrofluoric acid and soda ash (sodium carbonate), or caustic soda (sodium hydroxide). Control of pH is essential and proper agitation necessary to obtain the desired crystal size. The crystals are centrifuged, dried, sized, and packaged. Reactors are usually constmcted of carbon brick and lead-lined steel, with process lines of stainless, plastic or plastic-lined steel diaphragm, plug cock, or butterfly valves are preferred. 

W. Broadway, "A Pressure Sensitivity and Temperature Response Butterfly Valve for Cryogenic Service," paper presented at Energy Technology Conference and Exhibition, Houston, Nov. 5—9,1978. 

W. Broadway, "Development of Cryogenic Butterfly Valve Seat," paper presented atMJOE 71 st Mnnual Meeting Cyogenic Equipment Session, Miami, Nov. 12-16,1978. 

Example 6 Losses with Fittings and Valves It is desired to calculate the liquid level in the vessel shown in Fig. 6-15 required to produce a discharge velocity of 2 m/s. The fluid is water at 20°C with p = 1,000 kg/m and i = 0.001 Pa - s, and the butterfly valve is at 6 = 10°. The pipe is 2-in Schedule 40, with an inner diameter of 0.0525 m. The pipe roughness is 0.046 mm. Assuming the flow is tiirhiilent and taking the velocity profile factor (X = 1, the engineering Bernoulli equation Eq. (6-16), written between surfaces 1 and 2, where the... 

Contributing to f are losses for the entrance to the pipe, the three sections of straight pipe, the butterfly valve, and the 90 bend. Note that no exit loss is used because the discharged jet is outside the control volume. Instead, the V v2 term accounts for the kinetic energy of the discharging stream. The Reynolds number in the pipe is... 

Valve bodies are also standardized to mate with common piping connections flanged, butt-weld end, socket-weld end, and screwed end. Dimensional information for some of these joints and class pressure-temperature ratings are included in Sec. 10, Process Plant Piping. Control valves have their own standardized face-to-face dimensions that are governed by ISA Standards S75.03, 04, 12, 14, 15, 16, 20, and 22. Butterfly valves are also governed by API 609 and Manufacturers Standardization Society (MSS) SP-67 and 68. 

Butterfly Valves These valves (Fig. 10-155) occupy less space in the line than any other valves. Relatively tight sealing without excessive operating torque and seat wear is accomphshed by a variety of methods, such as resilient seats, piston rings on the disk, and inclining the stem to limit contact between the portions of disk closest to the stem and the body seat to a few degrees of curvature. 

Fluid-pressure distribution tends to close the valve. For this reason, the smaller manually operated valves have a latching device on the handle, and the larger manually operated valves use worm gearing on the stem. This hydraulic unb ance is proportional to the pressure drop and, with line velocities exceeding 7.6 m/s (25 ft/s), is the principal component in the torque required to operate the valves. Compared with other valves for low-pressure drops, these valves can be operated by smaller hydrauhc cylinders. In this service butterfly valves with insert bodies for bolting between existing flanges with bolts that... 

Convert quarter turn butterfly valves into ball valves. 

Driving units shut down by closing the main stop valve and the steam turbine regulating valves and at the same time closing the butterfly valve upstream of the expander (closing time 2-3 sec)... 

Instead of using the expander main bypass valve for regenerator pressure eontrol, it is also possible to install a small bypass valve, say 30%, downstream of the expander inlet butterfly valve, bypassing to tlie expander exhaust line as shown in Figure 4-73. Although tills valve may not appear neeessary, it ean provide additional flexibility and proteetion. 

Figure 4-143 represents a computer-generated plot that demonstrates the effectiveness of eddy current brakes in preventing overspeed of the string. The lower curve assumes the butterfly valve characteristic is linear from 60° open to the closed position. The rate of closure is 3.25 sec. (Butterfly valves are normally used to throttle the expander inlet gas.)... 

Trip speed is the speed at which an independent emergency device is activated and sends a signal to close the expander inlet butterfly valve system. This is approximately 105% of maximum continuous speed or synchronous speed (whichever is higher). 

Generally, butterfly valves are used for the inlet eontrol and bypass valves. Tliey are inexpensive to manufaemre, and their aemators are able to operate in aeeordanee witli tlie requisite response times. Butterfly valves do, however, have the disadvantage of a tightly eurved eharaeteristie. 

Step 6 Calculate step on the inlet valve. Now that the new inlet valve e after the breaker opening has been determined, this ean be translated into a valve position. This is a simple proeess using the valve eharaeteristie of the manufaeturer. Eigure 7-8 shows a typieal butterfly valve eharaeteristie. This eurve shows the ealeulated Using the valve eurve, the new valve position is determined. 

However, when an expander has to operate at mismatehed eondi-tions, the aetual mismateh usually oeeurs in the inlet butterfly valve, whieh attempts to maintain regenerator pressure. Fortunately, proeessing parameters ean also be modulated under different produetion eapaeities. In sueh eireumstanees, it is important to keep the volume flow in the normal range to maintain system effieieney. For an ideal gas, the eonditional equation is ... 

When actual mass flow through the expanders is lowered, efficiency varies according to power loss, deflective angle of gas in the leading edge of the rotating blades, and pressure drop across the inlet butterfly valve. The pressure drop increases as the valve closes. 

For partial condenser systems, the pressure can be controlled by manipulating vapor product or a noncondensible vent stream. This gives excellent pressure control. To have a constant top vapor product composition, the condenser outlet temperature also needs to be controlled. For a total condenser system, a butterfly valve in the column overhead vapor line to the condenser has been used. Varying the condenser cooling by various means such as manipulation of coolant flow is also common. 

Used for small duties, clean process, and only infrequent cleaning required. Vaporization is usually less than 30%, but less than 15% if the fractionator pressure is below 50psig. The viscosity of the reboiler feed should be less than 0.5 cp. Put a butterfly valve in the reboiler inlet piping. This type is used in nearly 100% of chemical plant thermosyphon applications (70% of petrochemical). 

Faclors lor butterfly valves assume minimum Ihroltling at design condlllens. II heavy throllhng is required, factors should be doubled... 

A butterfly valve in the line to the first stage seal drum limits the maximum flow to the first stage burner. The valve is set by observing the burners while flaring at design capacity. Once adjusted, the valve should be locked in position. 

A suction pressure throttling valve can also be installed to protect the compressor from too high a suction pressure. This is typically a butterfly valve that is placed in the suction piping. As flow rate to the compressor increases, the valve will close slightly and maintain a constant suction pressure. This will automatically limit the flow rate to exactly that rate where the actual volume of gas equals that required by the cylinder at tlie chosen suction pressure setting. It will not allow the suction pressure to increase and the compressor cylinder to thus handle more flow rate. 

Butterfly valves are particularly useful in low-pressure produced water service and as gas throttling valves on the inlets of compressors. 

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