04. November 2014 · Comments Off · Categories: Check Valves

Check valves

check valveclack valvenon-return valve or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction.

Check valves are “automatic” valves that open with forward flow and close with reverse flow. The pressure of the fluid passing through a system opens the valve, while any reversal of flow will close the valve. Exact operation will vary depending on the type of Check valve mechanism. Most common types of Check valves are swing, lift (piston and ball), butterfly, stop and tilting-disk.

An important concept in check valves is the cracking pressure which is the minimum upstream pressure at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure.

 

Types of Check valves

ball check valve is a check valve in which the closing member, the movable part to block the flow, is a spherical ball. In some ball check valves, the ball is spring-loaded to help keep it shut. For those designs without a spring, reverse flow is required to move the ball toward the seat and create a seal. The interior surface of the main seats of ball check valves are more or less conically-tapered to guide the ball into the seat and form a positive seal when stopping reverse flow.

 

Swing Check valves
A basic swing Check valve consists of a valve body, a bonnet, and a disk that is connected to a hinge. The disk swings away from the valve-seat to allow flow in the forward direction, and returns to valve-seat when upstream flow is stopped, to prevent backflow.The disc in a swing type Check valve is unguided as it fully opens or closes. There are many disk and seat designs available, in order to meet the requirements of different applications. The valve allows full, unobstructed flow and automatically closes as pressure decreases. These valves are fully closed when flow reaches zero, in order to prevent backflow. Turbulence and pressure drop in the valve are very low.
Swing Check valve

 

Lift Check valve
The seat design of a lift-Check valve is similar to a Globe valve. The disc is usually in the form of a piston or a ball.Lift Check valves are particularly suitable for high-pressure service where velocity of flow is high. In lift Check valves, the disc is precisely guided and fits perfectly into the dashpot. Lift Check valves are suitable for installation in horizontal or vertical pipe-lines with upward flow.

Flow to lift Check valves must always enter below the seat. As the flow enters, the piston or ball is raised within guides from the seat by the pressure of the upward flow. When the flow stops or reverses, the piston or ball is forced onto the seat of the valve by both the backflow and gravity.

Check valve Piston Type

 

03. November 2014 · Comments Off · Categories: China valve
Introduction to industrial Valves - Casting Materials
The following material are frequently used for cast steel gate valves,  globe valves and check valves and ball valves.
ASTM - Casting Materials

Common
Designation
ASTM
Casting
Specification
Service Recommendations
Carbon Steel ASTM A216
Grade WCB
Non-corrosive applications including water, oil and gases at temperatures between -20°F (-30°C) and +800°F (+425°C)
Low Temp
Carbon Steel
ASTM A352
Grade LCB
Low temperature applications to -50°F (-46°C). Not for use above +650°F (+340°C).
Low Temp
Carbon Steel
ASTM A352
Grade LC1
Low temperature applications to -75°F (-59°C). Not for use above +650°F (+340°C).
Low Temp
Carbon Steel
ASTM A352
Grade LC2
Low temperature applications to -100°F (-73°C). Not for use above +650°F (+340°C).
3.1/2% Nickel
Steel
ASTM A352
Grade LC3
Low temperature applications to -150°F (-101°C). Not for use above +650°F (+340°C).
1.1/4%Chrome
1/2% Moly Steel
ASTM A217
Grade WC6
Non-corrosive applications including water, oil and gases at temperatures between -20°F (-30°C) and +1100°F (+593°C).
2.1/4%Chrome ASTM A217
Grade C9
Non-corrosive applications including water, oil and gases at temperatures between -20°F (-30°C) and +1100°F (+593°C).
5%Chrome
1/2% Moly
ASTM A217
Grade C5
Mild corrosive or erosive applications as well as non-corrosive applications at temperatures between -20°F (-30°C) and +1200°F (+649°C).
9%Chrome
1% Moly
ASTM A217
Grade C12
Mild corrosive or erosive applications as well as non-corrosive applications at temperatures between -20°F (-30°C) and +1200°F (+649°C).
12% Chrome
Steel
ASTM A487
Grade CA6NM
Corrosive application at temperatures between -20°F (-30°C) and +900°F (+482°C).
12% Chrome ASTM A217
Grade CA15
Corrosive application at temperatures up to +1300°F (+704°C)
316SS ASTM A351
Grade CF8M
Corrosive or either extremely low or high temperature non-corrosive services between -450°F (-268°C) and +1200°F (+649°C). Above +800°F (+425°C) specify carbon content of 0.04% or greater.
347SS ASTM 351
Grade CF8C
Primarily for high temperature, corrosive applications between -450°F (-268°C) and +1200°F (+649°C). Above +1000°F (+540°C) specify carbon content of 0.04% or greater.
304SS ASTM A351
Grade CF8
Corrosive or extremely high temperatures non-corrosive services between -450°F (-268°C) and +1200°F (+649°C). Above +800°F (+425°C) specify carbon content of 0.04% or greater.
304L SS ASTM A351
Grade CF3
Corrosive or non-corrosive services to +800F (+425°C).
316L SS ASTM A351
Grade CF3M
Corrosive or non-corrosive services to +800F (+425°C).
Alloy-20 ASTM A351
Grade CN7M
Good resistance to hot sulfuric acid to +800F (+425°C).
Monel ASTM 743
Grade M3-35-1
Weldable grade. Good resistance to corrosion by all common organic acids and salt water. Also highly resistant to most alkaline solutions to +750°F (+400°C).
Hastelloy B ASTM A743
Grade N-12M
Is well suited for handling hydrofluoric acid at all concentrations and temperatures. Good resistance to sulphuric and phosphoric acids to +1200°F (+649°C).
Hastelloy C ASTM A743
Grade CW-12M
Good resistance to span oxidation conditions. Good properties at high temperatures. Good resistance to sulphuric and phosphoric acids to +1200°F (+649°C).
Inconel ASTM A743
Grade CY-40
Very good for high temperature service. Good resistance to spanly corrosive media and atmosphere to +800°F (+425°C).
Bronze ASTM B62 Water, oil or gas: up to 400°F. Excellent for brine and seawater service.
Common
Designation
ASTM
Casting
Specification
Service Recommended (by Relia Valve – China gate valve supplier)
02. November 2014 · Comments Off · Categories: Gate valves

Gate Valves

gate valve, also known as a sluice valve, is a valve that opens by lifting a round or rectangular gate/wedge out of the path of the fluid. The distinct feature of a gate valve is the sealing surfaces between the gate and seats are planar, so gate valves are often used when a straight-line flow of fluid and minimum restric­tion is desired.

Gate valves are primarily designed to start or stop flow, and when a straight-line flow of fluid and minimum flow restriction are needed. In service, these valves generally are either fully open or fully closed.

The disc of a Gate valve is completely removed when the valve is fully open; the disk is fully drawn up into the valve Bonnet. This leaves an opening for flow through the valve at the same inside diameter as the pipesystem in which the valve is installed. A Gate valve can be used for a wide range of liquids and provides a tight seal when closed.

On opening the gate valve, the flow path is enlarged in a highly nonlinear manner with respect to percent of opening. This means that flow rate does not change evenly with stem travel. Also, a partially open gate disc tends to vibrate from the fluid flow. Most of the flow change occurs near shutoff with a relatively high fluid velocity causing disk and seat wear and eventual leakage if used to regulate flow. Typical gate valves are designed to be fully opened or closed.When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low friction loss.

Construction of a Gate valve

Gate valves consists of three main parts: body, bonnet, and trim. The body is generally connected to other equipment by means of flanged, screwed or welded connections. The bonnet, which containing the moving parts, is attached to the body, usually with bolts, to permit maintenance. The valve trim consists of the stem, the gate, the disc or wedge and the seat rings.

Types of a Gate valve

The gate valves are normally classified as wedge gate valves (generally called cast steel gate valves), knife gate valves and slab gate valves and forged steel gate valves.

The gate valves can be classified as  API 6D gate valves, API 600 gate valves and  API 602 gate valves.

Discs of a Gate valve

Gate valves are available with different discs or wedges. Ranging of the Gate valves (made by China gate valve supplier) is usually made by the type of wedge used. The gate faces can form a wedge shape or they can be parallel.

The most common were:

  • Solid wedge is the most commonly used disk by its simplicity and strength.
    A valve with this type of wedge can be installed in each position and it is suitable for almost all liquids. The solid wedge is a single-piece solid construction, and is practically for turbulent flow.
  • Flexible wedge is a one-piece disc with a cut around the perimeter to improve the ability to correct mistakes or changes in the angle between the seats.
    The reduction will vary in size, shape and depth. A shallow, narrow cut gives little flexibility but retains strength.
    A deeper and wider cut, or cast-in recess, leaves little material in the middle, which allows more flexibility, but compromises strength.
  • Split wedge is self-adjusting and selfaligning to both seats sides. This wedge type consists of two-piece construction which seats between the tapered seats in the valve body. This type of wedge is suitable for the treatment of non-condensing gases and liquids at normal temperatures, particularly corrosive liquids.
  • Most common wedges in Gate valves

    Most common wedges for Gate valves

Stem of a Gate valve

The stem, which connects the handwheel and disk with each other, is responsible for the proper positioning of the disc. Stems are usually forged, and connected to the disc by threaded or other techniques. To prevent leakage, in the area of the seal, a fine surface finish of the stem is necessary.

Gate valves are classified as either:

  • Rising Stem
  • Non Rising Stem

For a valve of the Rising Stem type, the stem will rise above the handwheel if the valve is opened. This happens, because the stem is threaded and mated with the bushing threads of a Yoke. A Yoke is an integral part from a Rising Stem valve and is mounted to the Bonnet.

For a valve of the non Rising Stem type, there is no upward stem movement if the valve is opened. The stem is threaded into the disk. As the handwheel on the stem is rotated, the disk travels up or down the stem on the threads while the stem remains vertically stationary.

In the main Menu “Valves” you will find links to detailed (large) drawings of both stem types.

Seats of a Gate valve

Seats for Gate valves are either provided integral with the valve body or in a seat ring type of construction. Seat ring construction provides seats which are either threaded into position or are pressed into position and seal welded to the valve body. The latter form of construction is recommended for higher temperature service.

Integral seats provide a seat of the same material of construction as the valve body while the pressed-in or threaded-in seats permit variation. Rings with hard facings may be supplied for the application where they are required.

Advantages and disadvantages of Gate valves

Advantages:

  • Good shutoff features
  • Gate valves are bidirectional and therefore they can be used in two directions
  • Pressure loss through the valve is minimal

Diaadvantages:

  • They can not be quickly opened or closed
  • Gate valves are not suitable for regulate or throttle flow
  • They are sensitive to vibration in the open state

By Kevein from Zhejiang Relia Valve Co., Ltd. professional China valve supplier, China wafer check valve and China metal seated ball valve supplier

02. November 2014 · Comments Off · Categories: BALL VALVE

Ball valves

ball valve is a valve with a spherical disc, the part of the valve which controls the flow through it. The sphere has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends of the valve, and flow is blocked. The handle or lever will be inline with the port position letting you “see” the valve’s position. The ball valve, along with the butterfly valve and plug valve, are part of the family of quarter turn valves.

A Ball valve is a quarter-turn rotational motion valve that uses a ball-shaped disk to stop or start flow. If the valve is opened, the ball rotates to a point where the hole through the ball is in line with the valve body inlet and outlet. If the valve is closed, the ball is rotated so that the hole is perpendicular to the flow openings of the valve body and the flow is stopped.

Ball valves are durable and usually work to achieve perfect shutoff even after years of disuse. They are therefore an excellent choice for shutoff applications (and are often preferred to globe valves and gate valves for this purpose). They do not offer the fine control that may be necessary in throttling applications but are sometimes used for this purpose.

Ball valves are used extensively in industrial applications because they are very versatile, supporting pressuresup to 1000 bar and temperatures up to 752°F (500°C) depending on the ball valve design and material. Sizes typically range from 0.2 to 48 inches (0.5 cm to 121 cm). They are easy to repair and operate.

The body of ball valves may be made of metal, plastic, or metal with a ceramic center. The ball is often chrome plated to make it more durable.

Small Size Forged Floating Ball Valve With Nipple

Types of Ball valves

Ball valves are basically available in three versions: full port, venturi port and reduced port. The full-port valve has an internal diameter equal to the inner diameter of the pipe. Venturi and reduced-port versions generally are one pipe size smaller than the line size.

Ball valves are manufactured in different body configurations and the most common are:

The valve ends are available as butt welding, socket welding, flanged, threaded and others.

Materials – Design – Bonnet

Materials

Balls are usually made of several metallics, while the seats are from soft materials like Teflon®, Neoprene, and combinations of these materials. The use of soft-seat materials imparts excellent sealing ability. The disadvantage of soft-seat materials (elastomeric materials) is, that they are not can be used in high temperatures processes.

For example, fluorinated polymer seats can be used for service temperatures from −200° (and larger) to 230°C and higher, while graphite seats may be used for temperatures from ?° to 500°C and higher.

Stem design

The stem in a Ball valve is not attached to the ball. Usually it has a rectangular portion at the ball, and that fits into a slot cut into the ball. The enlargement permits rotation of the ball as the valve is opened or closed.

Ball valve Bonnet

The Bonnet of a Ball valve is fastens to the body, which holds the stem assembly and ball in place. Adjustment of the Bonnet permits compression of the packing, which supplies the stem seal. Packing material for Ball valve stems is usually Teflon® or Teflon-filled or O-rings instead of packing.

 

Ball valves applications

The following are some typical applications of Ball valves:

ball valve

ball valve

  • Air, gaseous, and liquid applications
  • Drains and vents in liquid, gaseous, and other fluid services
  • Steam service

Advantages and disadvantages of Ball valves

Advantages:

  • Quick quarter turn on-off operation
  • Tight sealing with low torque
  • Smaller in size than most other valves

Diaadvantages:

  • Conventional Ball valves have poor throttling properties
  • In slurry or other applications, the suspended particles can settle and become trapped in body cavities causing wear, leakage, or valve failure.