Fc Valves Bonnet

Gate Valve Sectional View

Gland

Gland packing

Bonnet

Bonnet gasket Body

Body seat ring Disc

Disc spring Disc facing ring

Fig. 7.28. Sectional view of a two-piece gate valve (British Valve Manufacturers Association, 1972).

g—Handwheel Bridge

Will the valve serve its chosen purpose? Is it suitable for aseptic operation or contained processes, and of the correct dimensions? Is the pressure drop across the valve tolerable? Will the valve withstand the rigours of the process? The materials used to construct the valve should be suited to the process. It is also important to know whether corrosive liquids are used or synthesized during the process. The maximum operating temperature and pressure of the process should be known. Are there welds or flanges in the valve? Is the valve one which can be operated by remote control?

The cost and availability of suitable valves. Can the valve be used for containment purposes?

Gland

Gland packing

Bonnet

Bonnet gasket Body

Body seat ring Disc

Disc spring Disc facing ring

Fig. 7.28. Sectional view of a two-piece gate valve (British Valve Manufacturers Association, 1972).

thread (rising stem), (b) a drilled sphere or plug, or a disc rotating in between two bearings or (c) a rubber diaphragm or tube which is pinched.

Gate valves

In this valve (Fig. 7.28), a sliding disc is moved in or out of the flow path by turning the stem of the valve. It is suitable for general purposes on a steam or a water line for use when fully open or fully closed and therefore should not be used for regulating flow. The flow path is such that the pressure drop is minimal, but unfortunately it is not suitable for aseptic conditions as mash solids can pack in the groove where the gate slides, and there may be leakage round the stem of the valve which is sealed by a simple stuffing box. This means that the nut around the stem and the packing must be checked regularly.

A wide range of valves is available, but not all of them are suitable for use in fermenter construction (Solomons, 1969; Kemplay, 1980).

The valves described in this section open and close by (a) raising or lowering the blocking unit with a screw

Globe valves

In this valve (Fig. 7.29), a horizontal disc or plug is raised or lowered in its seating to control the rate of

Globe Valve Gland Packing

Body

Fig. 7 29 Cilobe valve with outside screw and conventional disc tKcmphiy. 1980).

Handwheel Stem

One-piece gland Bonnet

-Gland packing

Bonnet gasket

Cover nut

One-piece gland Bonnet

-Gland packing

Bonnet gasket

Disc spring washer

Cover nut

Disc spring washer

Fig. 7.30. Piston valve (Kemplay, 1980).

Stainless steel piston fc^ ' Upper valve

M^ Lower valve

Fig. 7.30. Piston valve (Kemplay, 1980).

Needle valves

Body

Fig. 7 29 Cilobe valve with outside screw and conventional disc tKcmphiy. 1980).

(low. This type of valve is very commonly used for regulating the flow of water or steam since it may be adjusted rapidly. It is not suitable for aseptic operation because of potential leakage round the valve stem, which is similar in design to that of the gate valve. There is a high-pressure drop across the valve because of the flow path.

In both the gate and globe valves it is possible to incorporate a flexible metallic membrane around the stem of the valve, to replace the standard packing. This modified type of valve can be operated aseptically, but is bigger and more expensive. Valves with non-rising stems have been used, but they are still potential sources of contamination.

The needle valve (Fig. 7.31) is similar to the globe valve, except that the disc is replaced by a tapered plug or needle fitting into a tapered valve seat. The valve can be used to give fine control of steam or liquid flow. Accurate control of flow is possible because of the variable orifice formed between the tapered plug and the tapered seat. The aseptic applications are very limited.

Piston valves

The piston valve (Fig. 7.30) is similar to a globe valve except that flow is controlled by a piston passing between two packing rings. This design has proved in practice to be very efficient under aseptic operation. It is important to sterilize them partly open so that steam can reach as far as possible into the valve body. There may be blockage problems with mycelial cultures. The pressure drop is similar to that of a globe valve.

Fig. 7.31. Needle valve for accurate control of flow rate (Kemplay, 1980).

Lubricant screw

Gland Gland packing

Cover

Orifice A

Lubricant screw

Cover

Gland Gland packing

Orifice A

Bodily Orifice

Body

Lubricant grooves

Plug

Body

Lubricant grooves

Plug

Fig. 7.32. Sectional view of lubricated taper plug valve (British Valve Manufacturers Association, 1972).

Plug valves

Butterfly valves

In this valve there is a parallel or tapered plug sitting in a housing through which an orifice, A, has been been machined. The valve shown in Fig. 7.32 is in the closed position. When the plug is turned through 90° the valve is fully open and the flow path is determined by the cross-sectional area of A, which may not be as large as that of the pipeline. This type of valve has a tendency to leak or seize up, but the use of lubricants and/or sealants may overcome these problems. If suitable packing sleeves (e.g. compressed asbestos) are incorporated into the valve it will be suitable for use in a steam line as it is quick to operate, has protected seals, a minimal pressure drop and a positive closure. It can also provide good flow control.

Ball valves

This valve (Fig. 7.33) has been developed from the plug valve. The valve element is a stainless-steel ball through which an orifice is machined. The ball is sealed between two wiping surfaces which wipe the surface and prevent deposition of matter at this point. The orifice in the ball can be of the same diameter as the pipeline, giving an excellent flow path. The valve is suitable for aseptic operation, can handle mycelial broths and can be operated under high temperatures and pressures. The pressure and temperature range is normally limited by the PTFE seat and stem seals.

The butterfly valve (Fig. 7.34) consists of a disc which rotates about a shaft in a housing. The disc closes against a seal to stop the flow of liquid. This type of valve is normally used in large diameter pipes operating under low pressure where absolute closure is not essential. It is not suitable for aseptic operation.

Pinch valves

In the pinch valve (Fig. 7.35) a flexible sleeve is closed by a pair of pinch bars or some other mechanism which can be operated by compressed air remotely or automatically. The flow rate can be controlled from 10 to 95% of rated flow capacity (Pikulik. 1976). The valve is suitable for aseptic operation with fermentation broths, even when mycelial, as there are no dead spaces in the valve structure, and the closing mechanism is isolated from the contents of the piping. Obviously, the sleeve of rubber, neoprene, etc., must be checked regularly for signs of wear.

Diaphragm valves

Like the pinch valve, the diaphragm valve (Fig. 7.36) makes use of a flexible closure, with or without a weir. It may also be fitted with a quick action lever. This

Handle adaptor Packing adjuster Stem seals

Handle adaptor Packing adjuster Stem seals

Cross Section View Ball Valve

Body end

Seats

Fig. 7.33. Sectional view of end-entry ball valve (British Valve Manufacturers Association, 1972).

Body end

Seats

Body gasket

Trunnion

Bearing

Fig. 7.33. Sectional view of end-entry ball valve (British Valve Manufacturers Association, 1972).

Disc

Seat

Disc

Seat

Butterfly Valve Manufacturers

Shaft

Fig. 7.34. Sectional view of wafer-pattern butterfly valve (British Valve Manufacturers Association, 1972).

Shaft

Piston Valve Kemplay

Open

Shut

Fig. 7.35. Sectional view of pinch valve in open and shut position: (1) body; (5) flexible tube; (7) spindle; (8) top pinch bar; (9) lower pinch bar (British Valve Manufacturers Association, 1966; Kem-play, 1980).

Open

Shut

Fig. 7.35. Sectional view of pinch valve in open and shut position: (1) body; (5) flexible tube; (7) spindle; (8) top pinch bar; (9) lower pinch bar (British Valve Manufacturers Association, 1966; Kem-play, 1980).

Fig. 7.36. Sectional views of weir-type diaphragm valves in open and closed positions (Thielsch, 1967).

Fig. 7.34. Sectional view of wafer-pattern butterfly valve (British Valve Manufacturers Association, 1972).

valve is very suitable for aseptic operation provided that the diaphragm is of a material which will withstand repeated sterilization. The valve can be used for ON/OFF, flow regulation, and for steam services within

Fig. 7.36. Sectional views of weir-type diaphragm valves in open and closed positions (Thielsch, 1967).

pressure limits. Diaphragm failure, which is often due to excessive handling, is the primary fault of the valve. Ethylene propylene diene modified (EPDM) is now the preferred material. Hambleton et al. (1991) consider that a diaphragm valve with a steam seal on the 'clean' side (APV Ltd, Crawley, U.K.) is a potentially safer valve. However their widescale use would make a fermentation plant much more complex and expensive. Steam barriers on valves have been used by ICI pic for the 'Pruteen' air-lift fermenter (Smith, 1980; Sharp, 1989).

The most suitable valve

Among these group of valves which have just been described, globe and butterfly valves are most commonly used for ON/OFF applications, gate valves for crude flow control, needle valves for accurate flow control and ball, pinch or diaphragm valves for all sterile uses.

Needle Valve Kemplay 1980

Cover

Cover gasket Cover bolt

Hinge pin

Hinge

Disc

Body seat ring

Body

Fig. 7.37. Sectional view of swing check valve (Kemplay, 1980).

Cover

Cover gasket Cover bolt

Hinge pin

Hinge

Disc

Body seat ring

Body

Fig. 7.37. Sectional view of swing check valve (Kemplay, 1980).

Ball and diaphragm valves are now the most widely used designs in fermenter and other biotechnology equipment (Leaver and Hambleton, 1992). Although ball valves are more robust, they contain crevices which make sterilization more difficult.

Check valves pressure in the downstream side within defined limits irrespective of changes in the inlet pressure or changes in demand for gas, steam or water.

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