Self-actuated regulator VS Relief Valve

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Both the relief valve and the self-operated regulator are regulated by the pressure of the medium itself. The relief valve is controlled by the spring and the pressure area of the valve core corresponding to a relatively stable pressure, on the basis of the installation of a pilot pressure pipe in the valve head cylinder can adjust accurately the before and after valve pressure, that is, the self-operated regulator. Is there any difference between the self-actuated regulator and a relief valve?

  1. Different purpose. The self-operated regulator is intended to regulate while the relief valve is only for pressure reduction. The self-operated regulator is mainly to maintain the stability of pressure and pressure reducing valve is mainly to reduce the pressure to a safe value;
  2. The pressure reducing valve can be adjusted to the pressure manually. If the pressure in front of the valve changes greatly, frequent adjustment is needed. The self-operated control valve is automatic according to a set, objective value, the pressure can be constant after adjustment; If the pressure before and after the valve changes at the same time, the relief valve cannot automatically adjust to the fixed pressure, while the self-operated regulator can automatically maintain the back pressure or the pressure before the valve stable;
  3. The self-operated regulating valve can not only regulate the pressure before and after the valve but also control the differential pressure, temperature, liquid level, flow rate, etc. The relief valve can reduce the pressure after the valve only, single function;
  4. The adjusting accuracy of the relief valve is higher, generally 0.5, and the self-operated regulator is generally 8-10%;
  5. Different application. The self-operated regulator is widely used in petroleum, chemical industry and other industries. The relief valve is mainly used in water supply, fire control, heating and central air conditioning systems.

Generally speaking, the self-operated regulator is mainly used in the pipeline below DN80 and the pneumatic regulating valve is larger for pipe diameter. Relief valve needs to be equipped with a fixed set of valves because it is easy to leak, that is, the globe valve and the connecting valve are installed for maintenance and debugging at both ends of the control valve, and the relief valve and pressure gauge shall be set after pressure reducing.

What’s sluice gate valve?

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Similar with the knife gate valve in shape, the sluice gate valve is a type of manually screw operated gate, also known as a sluice gate valve. The sluice gate valve is mainly composed of frame, gate, screw, nut and other parts used for slurry and abrasive fluid systems. By turning the handwheel, the screw drives the screw nut and gate reciprocating along the horizontal direction to realize the opening and closing of the gate. Its installation is not limited by the Angle, easy to operate, but also to choose an actuator according to customer needs such as pneumatic, electric and so on. General installation flange on both sides can achieve different sizes of pipe installation.

Flange manual sluice gate valve is often used with an unloading device or hopper, generally a square sluice gate valve and circular sluice gate valve according to the shape of the inlet and outlet. Manual sluice gate valve is characterized by advantages of simple structure, reliable sealing, flexible operation, wear resistance, smooth passage, easy installation and disassembly. It is especially suitable for the transportation and flow regulation of water, slurry, powder, solid materials and block/lump materials less than 10mm, has been widely used in pulp and paper, cement industry, mining and food industry. It is an ideal device for where large changes in the control volume, frequent startup/shutdown, and rapid operation are required.

 

The installation tips of sluice gate valve

  1. Check the valve chamber and sealing surface, and no dirt or sand is allowed before installation;
  2. Flange bolt connection shall be tightened evenly;
  3. The packing part shall be pressed to ensure the sealing property of the packing and flexible opening of the gate;
  4. Check the valve model, connection size and medium flow direction before installation to ensure that they are consistent with the requirements reserve the necessary space for the valve actuator;

 

The common specification of sluice gate valve

Type A×A B×B C×C H L n-d Weight
One-way 200×200 256×256 296×296 820 100 8-Φ12 62
250×250 306×306 346×346 930 100 8-Φ14 70.5
300×300 356×356 396×396 1050 100 8-Φ14 81
400×400 456×456 496×496 140 100 12-Φ14 114
450×450 510×510 556×556 1450 120 12-Φ18 130
500×500 560×560 606×606 1610 120 16-Φ18 147
Two -way

 

 600×600 660×660 706×706 1830 120 16-Φ18 169
700×700 770×770 820×820 2130 140 20-Φ18 236
800×800 870×870 920×920 2440 140 20-Φ18 303
900×900 974×974 1030×1030 2660 160 27-Φ23 424
1000×1000 1074×1074 1130×1130 2870 160 24-Φ23 636

 

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Types of check valve

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The check valve is a kind of valve that depends on the medium flow itself to open and close automatically to prevent the reverse flow, also known as the reverse valve, one-way valve, non-return valve(NRV) and backpressure valve. The purpose of the check valve is to prevent reverse flow of the medium, to prevent the pump and drive motor from reversing, and to prevent the release of the container medium. When the fluid flows in the specified direction, the pressure of the fluid causes the disc to open, but when the fluid flows in the opposite direction, the pressure of the fluid and the self-aligning disc work together on the seat to prevent backflow, and can also be used to supply the auxiliary system where the pressure may rise above the system pressure. According to the structure, the check valve can be divided into swing check valve, wafer check valve, lift check valve, vertical check valve, double check valve, butterfly check valve, ball type check valve, Y type check valve.

 

Swing check valve

Swing check valves are divided into single-disc, double-disc and multi-disc check valves. The round disc around the seat axis moves for rotary, flow resistance is small because of the streamlined valve inside the channel, suitable for low flow rate and flow is not often changed in large-caliber pipeline. To ensure that the disc reaches the seat face in the proper position each time, the disc is designed in a hinged mechanism so that the disc has sufficient swing space and is in full contact with the seat. The disc may be made entirely of metal, may be covered with leather and rubber, or made by cladding cover, that depending on performance requirements.

 

Lift Check Valves

Lifting check valve can be divided into vertical and straight through according to the structure. The lift check valve disc is located on the seat sealing face, similar to the globe valve, the fluid pressure causes the disc to rise from the seat sealing face, the medium backflow causes the disc to fall back to the seat and cut off the flow. A vertical lift check valve is generally used in a nominal 50mm horizontal pipe. Straight-through lift check valves can be installed in both horizontal and vertical pipelines. The bottom valve is generally only installed on the vertical pipe at the sump pump, and the medium flows from bottom to top. The sealing performance of lift check valve is better than that of swing check valve.

 

Butterfly check valve

Also known as the wafer check valve, generally, straight through, the butterfly check valve is suitable for low pressure, large diameter and installation are limited occasions. Because the butterfly check valve’s working pressure is not high, generally below 6.4mpa, but the nominal diameter can reach more than 2000mm.The installation position of the wafer type check valve is not restricted. It can be on the horizontal pipeline, or on the vertical or on the inclined pipeline.

 

Diaphragm check valve
The diaphragm check valve is suitable for pipeline that easy to produce water hammer, the diaphragm can be very good to eliminate the water hammer effect when the medium countercurrent. Limited by the material of diaphragm, the diaphragm check valve is generally used in low-pressure normal temperature pipelines, especially in the water pipeline. The working temperature of the medium is -20 ~ 120℃ and the working pressure is less than 1.6mpa, and the diameter can reach up to 2000mm. Due to its excellent waterproof performance, simple structure and low manufacturing cost, it has been widely used in recent years.

 

 

The overlay welding(hardfacing) for valve sealing

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Sealing surface is the key part of the valve, in the sealing surface surfacing welding a layer of a special alloy, that is, hard facing or overlaying, can improve the hardness of the valve sealing surface, wear resistance and corrosion resistance, reduce the cost, and improve the service life of the valve. The quality of the sealing surface directly affects the service life of valve. Choosing the material of the sealing surface reasonably is one of the important ways to improve the service life of the valve. If you want to obtain the required valve surfacing surface, it is necessary to select the appropriate base material (workpiece material) and welding method in strict accordance with the operating instructions and operating requirements.

 

Commonly used overlay welding alloys include cobalt-based alloys, nickel-based alloys, iron-based alloys and copper-based alloys. Cobalt-based alloy is most used in valves because of its good high-temperature performance, excellent thermal strength, wear resistance, corrosion resistance and heat resistance fatigue performance than that of iron or nickel-based alloy. These alloys can be made into the electrode, wire (including flux-cored wire), flux (transition alloy flux) and alloy powder, etc., using the methods like submerged arc automatic welding, manual arc welding, tungsten argon arc welding, plasma arc welding, oxygen-acetylene flame welding in all kinds of valve shell and sealing surface. The welding groove is shown in the following figure:

The materials used for overlay welding the valve sealing surface are electrode, welding wire or alloy powder, etc., which are generally selected according to the valve’s operating temperature, working pressure and corrosive medium, or the type of valve, sealing surface structure, sealing pressure and allowable pressure, or enterprise processing capacity and user requirements. Each valve is open and closed under different operating parameters, so different temperature, pressure, medium and valve sealing surface material has different requirements. The experimental results show that the wear resistance of the valve sealing surface material is determined by the structure of the metal material. Some metal materials with austenitic matrix and a small amount of hard structure have low hardness but good wear resistance. Valve sealing surface has a certain high hardness is to avoid hard sundries in the medium pad and scratch. Considering comprehensively, the hardness value HRC35~ 45 is appropriate.

 

Valve sealing surface and failure reasons：

Valve type Overlay  welding part Sealing surface type Failure reasons
Gate valve Seat, gate The plane face Abrasion – based, erosion
Check valve Seat, disc The plane face Impact and erosion
High-temp ball valve Seat pyramidal face Abrasion – based, erosion
Butterfly valve Seat pyramidal face Erosion
Globe valve Seat, disc Plane or pyramidal Erosion – based, abrasion
Pressure reducing valve Seat, disc Plane or pyramidal Impact and erosion

 

Due to the uneven temperature distribution of welds and the thermal expansion and cold contraction of weld metal, residual stress is inevitable during overlay welding. In order to relax the welding residual stress, stabilize the shape and size of the structure, reduce distortion, improve the performance of the base material and welded joints, further release of harmful gases in the weld metal especially hydrogen to prevent delayed cracking, heat treatment after overlay welding is necessary. Generally speaking, the transition layer to 550℃ low-temperature stress treatment and time depends on the base wall thickness. In addition, the carbide alloy layer requires low-temperature stress-free heat treatment at 650℃, with heating speed less than 80℃/h and cooling speed less than 100℃/h. After cooling to 200℃, cool slowly to room temperature.

 

What’s orifice valves and what’s used for?

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Orifice valve is a type of flow metering throttling device which can measure all single-phase fluid including water, air, steam, oil, etc., has been widely used in power plants, chemical plants, oil fields and natural gas pipelines. Its working principle is that when the fluid with certain pressure flows through the orifice part in the pipeline, the locally contracts flow rate increases and the pressure decreases, resulting in the differential pressure. The greater the fluid flow velocity, the greater the differential pressure. There is a definite functional relationship between them and the fluid flow can be obtained by measuring the differential pressure.

Orifice flow system consists of an orifice throttling device, transmitter and flows computer. The flowrate measurement range of orifice flowmeter can be extended or transferred by adjusting the orifice opening diameter or the range of the transmitter within a certain range that can reach 100:1. It is widely used in situations with a large range of flow variations and can also calculate the bidirectional measurement of fluid.

 

Advantages and disadvantages of orifice valves

Advantages:

  • The throttling parts need not be calibrated, accurate measurement and the calibration measurement accuracy can be 0.5;
  • Simple and compact structure, small size and lightweight;
  • Wide application, including all single-phase fluid (liquid, gas, steam) and partial multi-phase flow;
  • The orifice plate with different apertures can be changed continuously with the change of flow rate and can be checked and replaced online.

Disadvantages：

  • There are requirements for the length of the straight pipe section, generally more than 10D;
  • Non-recoverable pressure drop and high energy consumption;
  • Flange connection is prone to leakage, which increases maintenance cost;
  • The orifice plate is sensitive to corrosion, wear and dirt, and may fail in the short term to heating water and gas (deviation with actual value)

 

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Ventilator valve, blow down valve and reverse flow valve for turbine system

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As a prime mover for large, high-speed operations, the steam turbine is one of the main devices in today’s coal-fired power plants, used to drag generators to convert mechanical energy into electrical energy. The steam turbine is characterized by a large volume and fast rotation. When it is transferred from the static state of normal temperature and pressure to high temperature and high-pressure high-speed operation, the regulating valve of the steam turbine plays a key role in stabilizing the speed and controlling the load. Only the stable and accurate operation of the valve can make the steam turbine work safely and efficiently. Today here we will introduce the three main valves like ventilator valve, blowdown valve and reverse flow valve for you, if interested, please read on.

 

Ventilator valve(VV)

When the middle-pressure cylinder of the unit starts to operate under low load, the high-pressure cylinder has no steam or less steam intake, and the vent valve is closed. This will cause the blade of the high-pressure stage to overheat due to friction blast. At this time, install a ventilation valve in the exhaust pipe of the high-pressure cylinder to keep the vacuum, similar to a blower, so that there is a little steam or air as possible in the high-pressure cylinder to reduce the blast. It connects the high-pressure cylinder with the condenser vacuum to prevent friction or excessive blast exhaust temperature when the load is low.

In addition, after the steam turbine trip, the ventilation valve automatically opens and the high-pressure cylinder steam quickly flow into the condenser, the turbine high-speed low-steam flow will have a blast of friction high tail blades to prevent because of the high-pressure steam pressure cylinder shaft seal leakage through high school into the intermediate pressure cylinder (the middle-pressure cylinder for vacuum) caused by rotor speed. It can also be used to prevent speeding.

In addition, after the steam turbine tripping, the ventilation valve automatically opens and the steam in the high-pressure cylinder is quickly discharged into the condenser. At the time of high-speed and low-steam, the air blast friction heat generated at the tail end of the high-pressure blade is reduced to prevent the steam from leaking into the middle-pressure cylinder (vacuum state) through the high-pressure cylinder shaft seal, resulting in the rotor Overspeed. It can also be used to prevent speeding.

High-pressure discharge ventilation valve is generally used in the unit in the middle-pressure cylinder or high-pressure cylinder combined with the beginning of the open to prevent air friction metal overheating (especially at the end of the high-pressure cylinder blade) caused by damage due to too little steam. In order to prevent over speed after slugging, some units can also open the ventilation valve to quickly drain the high exhaust steam. Some units also need a ventilation valve to take the heat away from the cylinder after the quick cooling after the shutdown, which is then discharged into the expanding container and finally into the condenser.

 

Blow down valve(BDV)

For high and middle-pressure cylinder units, in order to prevent the high-pressure cylinder and steam pipe tube of a small amount of steam channeling to the middle-pressure cylinder, the low-pressure cylinder, or the steam seal gap is large and the unit overspeed due to the steam seal tooth wear. Where a blow down valve（BDV） is installed. When the unit trips, the BDV valve opens quickly to direct the remaining steam from the high/medium pressure steam seal to the condenser to prevent the unit from overspeed. The opening and closure of blow down valve are controlled by the stroke of medium pressure regulating valve oil motor:

When the stroke of the oil motor of the middle pressure regulating valve is ≥30mm, the BDV valve is closed;

When the stroke of the middle pressure regulating valve oil motor is <30mm, the BDV valve opens.

The solenoid control valve provides a working magnetic field when compressed air enters the upper piston of the valve. When the electromagnetic control valve loses its magnetism, the upper part of the piston of the BDV valve is communicated with the exhaust and the air pressure is released. The piston moves up to open the valve under the action of the spring force.

 

Reverse flow valve (RFV)

There are no bearings between the high and medium pressure cylinders, which are communicated through the steam components of the rotor shaft seal. When the steam turbine is tripping under high load, the high and medium pressure regulating valve quickly closes and cuts off the steam turbine to prevent overspeed. However, at this time, the medium pressure cylinder is a vacuum, which causes the high-temperature/high-pressure steam of the high-pressure cylinder to return and leak from the shaft seal and continue to expand, thus causing overspeed. To prevent this from happening, a pneumatic BDV can be installed in operation when the pressure regulator valve closed, most of the leakage of steam directly to the exhaust device. When starting in a cold state, the auxiliary stream is led to the high-pressure discharge reverse valve through the RFV valve and discharged through the high-pressure inner cylinder steam trap and the high-pressure steam guide pipe steam trap.

 

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