Valve cost is up to 20 to 30% of the piping cost for a plant, depending on the process and the cost of a given type and size of valve can vary 100%, depending on its construction. Thus the selection of valves is extremely important to the economics, as well as operation, of process plants. The Process Engineer assumes the overall responsibility of establishing process design parameters of temperature, pressure, flow, start-up and shut-down procedures. The size of a valve is determined by the size of its ends which connect to the pipe. Port size may be smaller. Depending on the size of the required valve and availability, selection of stem type can be based on :

1. Whether it is undesirable for the conveyed fluid to be in contact with the thread bearing surface.

2. Whether an exposed screw is liable to be damaged by abrasive atmospheric dust.

3. Whether it is necessary to see whether the valve is open or closed. In addition to these most other valves have a simple rotary stem. Rotary, Ball, Plug, and Butterfly valves have a rotary stem which is moved by a permanent lever, or tool applied to a square boss at the end of the stem.

1. Disc, Seat and Port : These components are directly used for stopping and regulating the flow. The moving part directly affecting the flow is termed as disc, regardless of its shape. The non-moving part it bears on, is termed as the seat. The port is the maximum internal opening for flow (that is, when the valve is fully open). Discs may be actuated by conveyed fluid or be moved by stem having a linear, rotary or helical movement. The stem can be moved manually or be driven hydraulically, pneumatically or electrically, under remote or automatic control, or mechanically by weighted lever, springs etc.

2. Stem : There are two types of screwed stems, the rising stem and non-rising stem. These are moved by hand-lever or hand-wheel. Rising Stem (generally for gate and globe valves) are made either with inside screw (IS) or outside screw (OS). The OS type has a yoke on the bonnet and the assembly is referred to as outside screw and yoke (OS and Y). The hand-wheel can either rise with the stem, or the stem can rise through the hand wheel. Non-rising stem valves are of Gate type. The hand wheel and the stem are in the same position whether the valve is open or closed. The screw is inside the bonnet and in contact with conveyed fluid. A "Floor Stand" is a stem extension for use with both types of stem, where it is necessary to operate a valve through a floor or platform. Alternately, rods fitted with universal joints may be used to bring a valve hand wheel within an operator's reach. Depending on the size of the required valve and availability, selection of stem type can be based on :

   • Whether it is undesirable for the conveyed fluid to be in contact with the threatened bearing surfaces.

   • Whether an exposed screw is liable to be damaged by abrasive atmospheric dust.
   • Whether it is necessary to use if the valve is open or closed.

   In addition to the preceding types of stem used with gate and globe valves, most other valves have a simple rotary stem. Rotary-ball, plug and butterfly valves have a rotary stem which is moved by a permanent lever, or tool applied to a square boss at the end of the stem.

3. Bonnet : There are three basic types of attachments for valve bonnets: screwed (including union), bolted and breech lock. A screwed bonnet may occasionally stick and turn when a valve is opened. Although sticking is less of a problem with the union type bonnet, valves with screwed bonnets are best reserved for services presenting no hazard to personnel. Union bonnets are more suitable for small valves requiring frequent dismantling than the simple screwed type. The bolted bonnet has largely displaced screwed and union bonnet valves in hydrocarbon applications. A U-bolt or clamp type bonnet is offered on some small gate valves for moderate pressures, to facilitate frequent cleaning and inspection. The pressure seal is a variation of bolted bonnet used for high pressure valves, usually combined with OS and Y construction. It makes use of line pressure to tighten and seal an internal metal ring or gasket against the body. A critical factor for valves used for process chemicals is the lubrication of the stem. Care needs to be taken for selection of packing, gland design and choice of lubricant. As an option the bonnet may include a Lantern Ring which serves two purposes, either to act as a collection point to drain off any hazardous seepages, or as a point where lubricant can be injected. The breech lock is a heavier infrequently used and more expensive construction, also for high pressure use, and involves seal welding of the bonnet with the body.

4. Body : The selection of material to fabricate the interior of the valve body is important with a valve used for process chemicals. There is often a choice with regard to the body and trim, and some valves may be obtained with the entire interior of the body lined with corrosion- resistant material. Valves are connected to pipe, fittings or vessels by their body ends, which may be flanged, screwed, butt or socket welding, or finished for hose, sleeve coupling. Jacketed valves are also available.

5. Seal : In most stem operated valves, whether the stem has rotary or linear movement, packing or seals are used between stem and bonnet (or body). If high vacuum or corrosive, flammable or toxic fluid is to be handled, the disc or stem may be sealed by metal bellows, or by a flexible diaphragm (the later is termed pack-less construction). A gasket is used as seal between a bolted bonnet and valve body. Flanged valves use gaskets to seal against the line flanges. Butterfly valves may extend the resilient seat to also serve as line gaskets. The pressure-seal bonnet joint utilizes the pressure of conveyed fluids to tighten the seal.

6. Operator : This is a device which opens or closes a valve. Different devices are available.

   • Manual Operators

     • Hand lever : It is used to actuate the stems of small butterfly, ball, plug valves and cocks. Wrench operation is used for cocks and small plug valves.

     • Hand Wheel : It is the most common means of rotating the stem on the majority of popular smaller valves such as gate, globe and diaphragm. Additional operating torque for gate and globe valves is offered by hammer blow or impact hand wheels which may be substituted for normal hand wheels, if easier operation is needed but where gearing is unnecessary.

     • Chain : It is used where a hand wheel would be out of reach. The stem is fitted with a chain wheel or wrench (for lever operated valves) and loop of the chain is brought within one meter of working floor level. Universal type chain wheels which attach the regular hand wheel have been blamed for accidents, in corrosive atmospheres, where an infrequently operated valve has stuck, the attaching bolts have been known to fail. This problem does not arise with the chain-wheel that replaces the regular valve hand-wheel.

     • Gear : These are used to reduce the operating torque. For manual operation, it consists of a hand wheel operated gear train actuating the valve stem. As a guide, gear operators should be considered for valves of 350 mm NB and larger up to 300#, 200 mm NB and larger up to 600#, 150 mm NB and larger up to 1500# and 100 mm NB and larger for higher ratings.

   • Powered Operators

     • Electric Geared Motor : The valve stem is moved by Geared Motor. This is useful for operating large valves in remote areas.

     • Solenoid : These can be used for fast acting check valves, and with on/off valves in light-duty instrumentation applications.

     • Pneumatic and Hydraulic : These may be used where flammable vapor is likely to be present. They are of following forms:

       • Cylinder with double acting piston driven by air, water, oil or other liquid which usually actuates the stem directly.

       • Air motor which actuates the stem through gearing. These motors are commonly piston and cylinder radial type.

       • A double acting vane with limited rotary movement in a sector casing, actuating the stem directly.

       • Squeeze type.
   
   Gate Valve : There are different types of gate valves.

   1. Plug Gate Valves : This valve has round tapered disc which moves up and down. Suitable for throttling and full flow use, but only available in smaller sizes.

   2. Single Disc Parallel Seat Gate Valve : Unlike single seat valve described above, this valve affords closure with flow in either direction. Stresses on stem and bonnet are lower than wedge gate valves. It is primarily used for liquid hydrocarbons and gases.

   3. Single Disc Single Seat Gate Valve or Slide Valve: It is used for handling paper pulp slurry and other fibrous suspensions, and for low pressure gases. It will not function properly with inflow on the seat side. It is suitable for regulating if tight closure is not required.

   4. Double Disc (Split Wedge) Gate Valve : In this discs wedge against inclined seats without use of a spreader. Other features are same as parallel seat. It allows the disc to rotate, distributing wear.

   5. Double Disc Parallel Seat Gate Valve : It has two parallel discs which are forced on closure, against parallel seats by a spreader. It is used for liquids and gases at normal temperatures. Unsuitable for regulation. To prevent jamming it is installed vertically.

   6. Solid Wedge Gate Valve : It has either solid or flexible wedge disc. In addition to on/off service, these valves can be used for regulating usually in sizes of 150 mm NB and larger, but it will make noise unless disc is fully guided throughout travel. Suitable for most liquids and gases.

   
   

   SIZES OF 150# GATE VALVES

   SIZE NB	LENGTH	DIAMETER	FLANGE THICKNESS	HANDLE DIA	HEIGHT
   40	165	127	14.3	152	330
   50	178	152.5	16	203	360
   65	190.5	178	17.5	203	415
   80	203	190.5	19	254	425
   100	229	229	24	254	510
   125	254	254	24	305	595
   150	267	279.5	25.4	305	685
   200	292	343	28.6	305	773
   250	330	406.5	30.5	408	940
   300	356	483	32	457	1030
   350	381	533.5	36	457	1270
   400	406.5	597	36.5	508	1450
   450	432	635	40	508	1600
   500	457	698.5	43	610	1810
   600	508	813	48	610	2170

   MATERIALS OF CONSTRUCTION

   BODY

   CARBON STEEL CARBON STEEL FORGED A-105 CARBON STEEL CAST A-216 Gr WCB 0.15% MOLY STEEL CAST A-217 Gr WCI Cr. MOLY STEEL CAST A-217 Gr WC6, WC9 4.6% Cr. MOLY STEEL CAST A-217 Gr C5 8.1% Cr. MOLY STEEL CAST A-217 Gr C12 LOW CARBON STEEL CAST A-352 Gr LCB LOW CARBON MOLY STEEL CAST A-352 Gr LC-1 3.5 NICKEL STEEL CAST A-352 Gr LC-3  STAINLESS STEEL 18-8 S CAST A-351 Gr CF8 18-8 S MOLYCAST A-351 Gr CF8M 18-8 S LOW CARBON A-351 Gr CF3 18-8 S LOW CARBON WITH MOLY A-351 Gr CF3M 18-8 S Cb CAST A-351 Gr CF8C 1.25 Cr 0.5 MOLY FORGED A-182 GrF11 11.5-13.5 Cr STEEL FORGED A-182 Gr FC HEAT RESISTING 25-12 CAST A-297 Gr MH HEAT RESISTING 25-20 CAST A-297 Gr MK HEAT RESISTING 25-30 CAST A-297 Gr MT  NICKEL ALLOY NICKEL CAST A-296 CZ 100 MONEL CAST A-296 M35W HATELLOY B CAST A-296 N12M HASTELLOY C CAST A-296m M CW-12M

   
   
   • MANUFACTURING STANDARDS : BS:1414/API-600/API-6D/ANSI B-16.34
   • FACE TO FACE AS PER ANSI B 16.10
   • ENDS FLANGED & DRILLED AS PER ANSI B 16.5 RF
   • TESTED AS PER BS:5146, API 598
   • AVAILABLE IN CLASS 900, 1500
   • AVAILABLE WITH ACTUATOR OPERATOR
   • AVAILABLE WITH EXTENSION STEM

   TEST PRESSURE Kg/sq cm
   CLASS	HYDROSTATIC		AIR
   	BODY	SEAT &  BACK SEAT	SEAT
   150	30	22	6
   300	76	55	6
   600	150	110	6

   
   

   SIZES OF 300# GATE VALVES

   SIZE NB	LENGTH	DIAMETER	FLANGE THICKNESS	HANDLE DIA	HEIGHT
   40	190.5	156	21	152	390
   50	216	165	22	203	370
   65	241.5	190.5	25.4	203	440
   80	282.5	210	29	254	445
   100	305	254	32	254	520
   125	381	279.5	35	305	570
   150	403.5	317.5	36.5	356	740
   200	419	381	41.6	406	910
   250	457.5	444.5	48	458	1100
   300	502	521	51	508	1200
   350	762	584.5	54	559	1415
   400	838.5	648	57.5	610	1540
   450	914.5	711.5	60.5	813	1670
   500	991	775	63.5	965	1910
   600	1143	914.5	70	1508	GEAR

   
   

   SIZES OF 600# GATE VALVES

   SIZE NB	LENGTH	DIAMETER	FLANGE THICKNESS	HANDLE DIA	HEIGHT
   40	241.5	156	28.6	203	380
   50	292	165	32	203	445
   65	330	190.5	35	254	475
   80	356	210	38	254	490
   100	432	273	44.5	305	615
   125	508	330.5	51	406	765
   150	559	356	54	457	840
   200	660.5	419	62	508	950
   250	787.5	508	70	610	1290
   300	838.5	559	73	406	GEAR
   350	889	603.5	76.5	508	GEAR
   400	991	686	82.5	508	GEAR
   450	1093	743	89	508	GEAR
   500	1194	813	95.5	508	GEAR

   
   

   Plug Valve : It has a cylindrical or tapered plug in the body. Its advantage is that it is compact and a quarter turn valve. The tapered plug tends to jam and requires high operating torque. This is overcome to some extent by low-friction teflon seat or by lubrication (with the drawback that it may contaminate the conveyed fluid). It is mainly used for water, oil, slurries or gases as quick closing valve.
   

   Globe Valve : There are different types of Globe Valves.

   1. Blow Off Valve : It confirms to boiler codes. Y and angle types are often used. It is used to remove air and other gases from boilers. It is manually operated.

   2. Double Disc Globe Valve : It features two discs bearing on separate seats spaced apart on a single shaft, which frees the operator from stresses set up by the conveyed fluid pressing into the valve. It is principally used on control valves and pressure regulators for steam and other gases. Tight shut-off is not possible.

   3. Composition Disc Globe Valve : It is suitable for coarse regulation and tight shut off. Replacable composition disc construction is similar to that of a faucet. Grit will imbed in the soft disc preventing seat damage and ensuring good closure. Close regulating will rapidly damage the seat.

   4. Wye Body Globe Valve : It has in-line ports and stem emerging at about 45 deg, hence the name Y. It is preferred for erosive fluids due to smoother flow patterns.

   5. Plug Type Disc Globe Valve : It is used for severe regulating service with gritty liquids, such as boiler feed water, and for blow-off service. It is less subjected to wear under close regulation than the regular seated valve.

   6. Regular Disc Globe Valve : This is unsuitable for close regulation as disc and seat have narrow (almost line) contact.

   7. Angle Valve : This is globe valve with body ends at right angles, saving the use of a 90 deg elbow. However, higher stress may prevent its use.

   8. Straight Globe Valve : These are used for regulating service. For line sizes over 150 mm NB choice for flow control may go for gate or butterfly valve. The direction of flow around disc is in upward direction.

   SIZES OF 150# GLOBE VALVES

   SIZE NB	LENGTH	DIAMETER	FLANGE THICKNESS	HANDLE DIA	HEIGHT
   25	127	108	11.1	152	260
   40	165	127	14.3	152	300
   50	203	152.5	16	203	330
   65	216	178	17.5	203	334
   80	241.5	190.5	19	254	395
   100	292	229	24	305	470
   125	356	254	24	305	510
   150	406.5	279.5	25.4	356	570
   200	495.5	343	28.6	406	642
   250	622.5	406.5	30.5	406	768
   300	698.5	483	32	508	770
   350	787.5	533.5	35	508	920
   400	914.5	597	36.5	508	1010
   450	978	635	40	559	1062
   500	978	698.5	43	559	1220

   
   

   SIZES OF 300# GLOBE VALVES

   SIZE NB	LENGTH	DIAMETER	FLANGE THICKNESS	HANDLE DIA	HEIGHT
   25	203	124	17.5	152	295
   40	229	156	21	203	310
   50	267	165	22.2	203	325
   65	292	190.5	25.4	254	330
   80	317.5	210	28.6	254	450
   100	356	254	32	305	515
   125	400	279.5	35	356	530
   150	444.5	317.5	36.5	356	600
   200	559	381	41.5	356	730
   250	622.5	444.5	48	406	840
   300	711.5	521	51	508	1005

   
   

   SIZES OF 600# GLOBE VALVES

   SIZE NB	LENGTH	DIAMETER	FLANGE THICKNESS	HANDLE DIA	HEIGHT
   25	216	124	24	152	295
   40	241.5	156	28.6	203	310
   50	292	165	32	203	325
   65	330	190.5	35	254	381
   80	356	210	38	254	485
   100	432	273	44.5	305	623
   125	508	330.5	51	356	660
   150	559	356	54	356	778
   200	660.5	419	62	406	828
   250	787.5	508	70	508	942

   
   

   Needle Valve : It is small valve used for flow control and for dosing liquids and gases. Resistance to flow is precisely controlled by a relatively larger seat area and the adjustment afforded by fine threading of the stem.
   

   Squeeze Valve : It is well suited to regulating the flow of difficult liquids, slurries and powders. Maximum closure is about 80%, which limits the range of regulation, unless the variation of this type of valve with a central core (seat) is used, offering full closure.
   

   Pinch Valve : It is also suited to regulating flow of difficult liquids, slurries and powders. Complete closure is possible, but tends to rapidly wear the flexible tube, unless of special design.
   

   Ball Valve : Its advantages are low operating torque, availability in large sizes, rotary 90 deg stem movement, compactness, and in-line ability to replace of all wearing parts in some designs. Possible disadvantages are that liquid is trapped within the body (and within the disc on closure), and that compensation of wear is affected only by resilient material behind the seats, the later is avoided in single seat eccentric version, which has the ball slightly offset so that it presses into the seat, on closure. Principal uses are for water, oil, slurries, gases and vacuum. Valve is available with a ball having a shaped port for regulation.
   

   Butterfly Valves : This offers advantage of rotary stem movement (90 deg or less), compactness and absence of pocketing. It is available in all sizes, and can be produced in chemical-resistant and hygienic forms. The valves are used for gases, liquids, slurries, powders and vacuum. The usual resilient plastic seat has a temperature limitation, but tight closure at high temperatures is available with the version having metal ring seal around the disc. If the valve is flanged, it may be held between flanges of any type. Slip-on and screwed flanges do not form a proper seal with some wafer forms of the valve, in which the resilient seat is extended to serve also as line gaskets.
   

   Check Valve : There are different types of check valves.

   1. Wafer Check Valve : It affects closures by two semi-circular doors, both hinged to a central post in a ring-shaped body which is installed between flanges. It is frequently used for non-fouling liquids, as it is compact and relatively low cost. A single disc type is also available.

   2. Ball Check Valve : It is suitable for most services. The valve can handle gases, vapors and liquids, including those forming gummy deposits. The ball sits by gravity and/or back pressure, and is free to rotate, which distributes wear and aids in keeping contacting surfaces clean.

   3. Stop Check Valve : Its principal use is in steam lines, with steam generation by multiple boilers. It can be kept closed automatically or manually.

   4. Piston Check Valve : It changes the flow in 90 deg, and it also has a lifting disc. It has less pounding with frequent changes in flow direction. Spring loaded can operate in any orientation. It is not suitable for gritty liquids.

   5. Lift Check Valve : In this the disc is guided and it rises upward with fluid pressure, and closes by gravity. It can be installed horizontally or vertically if spring is provided to push the disc back.

   6. Tilting Disc Valve : It is suitable where frequent flow reversal occurs. Valve closes rapidly with better closure and less slamming than the swing check valve, which it somewhat resembles. It can be installed vertically with flow upward or horizontally.

   7. Swing Check Valve : The regular swing check valve is not suitable if there is frequent flow reversal as pounding and wearing of disc occurs. For gritty liquids, a composition disc is advisable to reduce damage to the seat. It may be mounted vertically with upward flow or horizontally.

   8. Foot Valve : It is typically used to maintain a head of water on suction side of a pump. The valve is basically a lift-check valve with a strainer integrated.

   
   

   SIZES OF 150# CHECK VALVES

   SIZE NB	LENGTH	DIAMETER	FLANGE THICKNESS	HEIGHT
   40	165	127	14.3	112
   50	203	152.5	16	138
   65	216	178	17.5	160
   80	241.5	190.5	19	170
   100	292	229	24	185
   125	330	254	24	215
   150	356	279.5	25.4	245
   200	495.5	343	28.6	305
   250	622.5	406.5	30.5	340
   300	698.5	483	32	400
   350	787.5	533.5	36	450
   400	864	597	36.5	470
   450	978	635	40	525
   500	978	698.5	43	559
   600	1296	813	48	650

   
   

   SIZES OF 300# CHECK VALVES

   SIZE NB	LENGTH	DIAMETER	FLANGE THICKNESS	HEIGHT
   40	241.5	155.5	21	140
   50	267	165	22.5	160
   65	292	190.5	25.4	180
   80	317.5	210	29	200
   100	356	254	32	225
   125	400	279.5	35	250
   150	444.5	317.5	36.5	265
   200	533.5	381	41.5	325
   250	622.5	444.5	48	390
   300	711.5	521	51	465
   350	838.5	584.5	54	470
   400	864	648	57.5	500
   450	978	711.5	60.5	580
   500	1016	775	63.5	675
   600	1346	914.5	70	775

   
   

   SIZES OF 600# CHECK VALVES

   SIZE NB	LENGTH	DIAMETER	FLANGE THICKNESS	HEIGHT
   40	241.5	155.5	28.6	160
   50	292	165	32	170
   65	330	190.5	35	190
   80	356	210	38	200
   100	432	273	44.5	235
   125	508	330.5	51	285
   150	559	356	54	325
   200	660.5	419	62	425
   250	787.5	508	70	500
   300	838.5	559	73	500
   350	889	603.5	76.5	590
   400	991	686	82.5	655
   450	1092.5	743	89	680
   500	1194	813	95.5	785

   
   

   Diverting Valves : Two types of diverting valves are made. Both switch flow from a line into one of two outlets. One type is of Y pattern with a hinged disc at the junction which closes one of the two outlets, and is used to handle powders and other solids. The second type handles liquids only, and has no moving parts. Flow is switched by two pneumatic control lines. It is available up to 150 mm NB.
   

   Multi Port Valves : It is used largely on hydraulic and pneumatic control circuits and sometimes used directly in process piping. These valves have rotary ball or plug type discs with one or more ports arranged to switch flow.
   

   Safety Valve : There are different types of safety valves.

   1. Ball Float Valve : These automatic valves can be used as air traps to remove water from air system, to remove air from liquid systems and act as vacuum breaker or breather valves, and to control liquid level in tank. These are not intended for removal of condensate.

   2. Safety Relief Valve : It relives excess pressure of either gas or liquid which may suddenly develop a vapor phase due to rapid and uncontrolled heating from chemical reaction in liquid-laden vessels.

   3. Relief Valve : It is used to relieve excess pressure in liquids, in situations, where full flow discharge is not required, when release of small volume of liquid would rapidly lower pressure. It is mounted vertically.

   4. Safety Valve : It is a rapidly opening (popping action) full flow valve for air and other gases. It is mounted vertically.

   
   

   Line Blind Valve : This is a positive shut-off device which basically consists of a flanged assembly, sandwiching a spectacle plate or blind. It is used where spectacle blind needs to be installed and removed frequently.
   

   Flush Bottom Valve : It is usually installed on tanks and vessels. These are usually globe type valves, designed to minimize pocketing, primarily for convenient discharging liquids from the low point of a tank.
   

   Sampling Valve : A valve usually of needle or globe pattern, placed in a branch line for the purpose of drawing off samples of process materials through a branch. Sampling from very high pressure lines is best done through a double valve collecting vessel. A cooling arrangement may be needed for sampling from high temperature lines.
   

   Control Valve : It automatically regulates pressure and/or flow rate, and are available for any pressure. If there are different system pressures, in a plant up to and including 300#, sometimes all control valves chosen will be rated at 300# for inter-changeability. The control valve is usually chosen to be smaller than size to avoid throttling and consequent rapid wear of the seat. Globe pattern valves are normally used for control, and their ends are usually flanged for ease of maintenance. The disc is moved by hydraulic, pneumatic, electrical or mechanical actuator.
   

   Pressure Regulating Valve : These are control valves of globe type which adjust downstream pressure of liquid or gas (including steam or vapor) to a lower desired value called set pressure.
   

   Diaphragm Valve : It is used for regulating flow of slurries and corrosive liquids and for vacuum. The term diaphragm valve is also applied to valves which have a diaphragm seal between stem and body, but these are better to as diaphragm seal or pack-less valves.
   

   Breather Valve : A special self acting valve installed on storage tanks, etc., to release vapor or gas on slight increase of internal pressure.