valves

Valves: Valves are used in the piping system to control the flow of fluids (liquid or gases) in the pipeline. They are basically classified according to

  1. Function
  2. Types of valves  
  3. Material of construction  
  • cast iron
  • Carbon steel
  • Low temp. Alloy steel.
  • High temp. alloy steel.
  • Stainless steel.)
  • Non-metallic material like P.V.C Polypropylene etc.     
  • d) Class(Pressure, temp, rating)
  • e) End connections. Flange ends socket weld and screwed end but weld ends. 
  • f) Methods of operation. 
  • Manual through handwheel
  • Gear operated
  • Pneumatic or motor operated.

a) Function:

  1. Isolation shut off. 
  2. Throttling or regulating flow.
  3. Prevention of backflow.
  4. Automatic control of flow.
  5. Relieving of excess pressure.
  6. Regulating the pressure.
  7. Changing the direction of flow
  8. Draining or venting the fluid from the piping system-  valves

1) Gate Valves:

valves

They function by the raising or lowering of wages or disk into the stream of flow. Gate valve with non-rising stem: In these types of values, the port is opened or closed by the travel of the lower end of the stem, screwing into the wedge. Hence their overall height is less than rising stem gate valves which make them suitable wherever space is limited. Another desirable feature is that, in a highly corrosive atmosphere, as may be encountered in many chemical plants, the threaded stem is less subjected to corrosive.

Rising stem gate valve: These are used wherever it is necessary for the operator to know at a glance whether the valve is in an open or closed position. In this type of valve, the threads in the stem engage with threads in the valve bonnet which makes stem and handwheel to rise of lower upon being turned-valves

Limitation of gate valve: 1)Gate valves are prone to vibration when in a partially open state and are also subject to seat and disc wear. 2) Some large size gate valves are not recommended for steam service. 3) Gate valves have slow response characteristics are require large actuating forces.

2) Ball valve:

valves

The ball valve is basically a ported sphere in housing. Rotation of the sphere by 90* charges the position from open to close. The ball may be fixed or floating design. Ball valves are available in a variety of sizes and with a wide choice of actuating mechanism-valves

Usage:

 Ball valves are used in a wide range of applications including flow control, pressure control, and shut off. They can be designed for use of corrosive fluids, very viscous fluids and slurries, in addition to normal liquids and gases. They can be used at high pressure and temperature – valves

Advantages:

Ball valves generally have a very low-pressure drop and low leakage. They are small in size and low in weight compared to other types with similar ratings. They are rapid opening and are rapidly closing.

Limitation:

The seat of ball valves is subject to extrusion if the valve is used for throttling fluid trapped in the ball in a closed position may cause problems if the ball is not vented. Because of quick opening, they may cause water hammer in the system or cause surge pressures which may be undesirable.

3) Butterfly valve:

valves

The typical butterfly valve consists of a disc that can rotate about a shaft in a housing. The disc closes against a ring seal to close off flow. Various actuating mechanisms such as the lever gear actuator are used to operate the valves.

Usage:

Butterfly valves are generally used in low-pressure system applications where the leakage is relatively unimportant. They are normally in large diameter lines.

Advantages:

1. Butterfly valves have a very low-pressure drop and are relatively lightweight. 2. The fact to face dimensions is usually quite small. The diameter of the valve can be of the same order as the diameter of the connecting pipes.

Limitations:

The leakage in a butterfly valve is fairly high unless special seals are often damaged by the high-velocity flow. These valves usually require high actuation forces and are generally limited to low pressure and low temperature.

4) Foot Valve:

The foot valve is used in the suction line of the pump. The main purpose of the foot valve is a suction line of the pump is full of the materials.

5) Air Release Valve:

1. Trapped in the pipeline or vacuum condition is very dangerous for fluid pipelines. These conditions can burst pipelines with disastrous consequences. An air valve automatically admits air in the pipelines and avoids vacuum condition 2. While filling the mains high-pressure air is exhausted avoiding air trap and backpressure condition. a) Single air valves:- are used for smaller pipelines up to 150mm. b) Double air valves:- are used for large size pipes. Double our valve with isolating valve allows servicing of the valve even on charged pipelines.

6) non-return valve (check valve) :

These are designed to permit the flow of fluid in one direction only. If a reversal of flow takes place, the valve automatically closes and prevents backflow along the line. There are three basic types of check valves i.e.

  1. a) Horizontal swing.
  2. b) Vertical (Lift OR Piston).
  3. c) Ball valve.

1. Swing check valves offer minimum resistance to flow.2. These are not recommended where a frequent reversal of flow occurs as this causes the valve to chatter. 3. Horizontal lift check valves are used in an application where the flow is irregular or subject to frequent reversal. 4. Ball check valves are made in horizontal angle and vertical design and are recommended in rapidly fluctuating flow, because of their noiseless operation.

7) Landing valves (Hydrant valve):

1. It is used as an outlet source of the fire hydrant lines as well as in fire vehicle.2. The following type of hydrant valve is available in the market.

  •  Single-headed Hydrant valve
  • Double-headed Hydrant valve
  • The oblique threaded Hydrant valve
  • Straight threaded Hydrant valve.
  • Right-angled Hydrant valve
  • Straight flared Hydrant valve
  • The outlet of the hydrant valve is 38.50 or 63 mm.
  1. It is made from gunmetal, light-alloy with cast iron brass hand wheels tested at 21kg/cm2
  2. Indian specification JS 5290.
  3. In non-working position the outlet is closed with a blank cap, which made from plastic or brass with a clown.

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