What is an orifice valve

What is an orifice valve?

Orifice valve is a new type of flow metering and throttling device. Orifice valve is the most widely used flow meter in the world. Orifice valve is suitable for flow measurement of natural gas, oil, gas, water and other gases and liquids with or without sulfur. It is widely used in energy, petroleum, chemical and metallurgical industries.

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The research on standard throttling device is worldwide, and its depth is unmatched by other flow meters. It is because of the abundant data and statistical data accumulated in the experimental research that this kind of flowmeter does not need actual flow calibration, and the overall accuracy of the flowmeter can be obtained by dry calibration method, which is the only one in all flow meters. Many years of application experience and field comparison show that the orifice flowmeter is very stable and reliable. The installation and calibration of orifice flowmeter must be carried out in strict accordance with the relevant national standard (GB / T2624-1993).
The orifice flowmeter consists of orifice throttling device, transmitter and flow calculation unit. With the continuous development of computer technology, the performance and accuracy of transmitter, flow computer and other instruments have been greatly improved. Therefore, the range of orifice flowmeter can be very wide, even up to 100:1.
The flow measurement range of orifice flowmeter can be expanded or transferred by adjusting the orifice diameter or the range of matched transmitter. Other types of flow meters can only be replaced when they are beyond the measuring range. This characteristic of orifice flowmeter is widely used in the occasions where the measured flow varies in a large range.
The orifice flowmeter with symmetrical orifice as throttling element, equipped with corresponding transmitter and flow calculation unit, can also realize two-way flow measurement.

Performance characteristics

  • 1. The standard throttling element is fully used and recognized by the international standards organization. It can be put into use without real flow calibration and is the only one in the flowmeter;
  • 2. The structure is easy to copy, simple, firm, stable and reliable, and the price is low;
  • 3. Wide range of applications, including all single-phase fluid (liquid, gas, steam), part of the mixed phase flow, general production process pipe diameter, working state (temperature, pressure) all have products;
  • 4: detection parts and differential pressure display instruments can be produced by different manufacturers separately, which is convenient for professional scale production.

Working principle of orifice valve

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When the fluid filled the pipe flows through the throttling device in the pipe, the flow beam will form a local contraction at the throttling part, so that the flow rate will increase and the static pressure will decrease, resulting in the static pressure difference (differential pressure) before and after the throttling part. The greater the flow velocity is, the greater the differential pressure is. There is a definite functional relationship between the differential pressure and the flow rate. According to the above functional relationship, the fluid flow can be measured by measuring the differential pressure value.

Purpose of orifice valve

  • 1. Simple orifice valve: the accuracy is higher than that of clip type orifice throttling device, and the measurement accuracy is accurate. The calibrated measurement accuracy can be up to grade 1; it is the best device delivered by both the supplier and the demander. The lifting mechanism without orifice plate can complete the inspection and replacement of orifice plate only when the medium conveying is stopped; the structure is simple and the cost is low. The sealing is reliable, safe and economical, and the floor space is small, so there is no need to set bypass pipeline.
  • 2. Advanced orifice valve: it has higher accuracy than conventional valve type throttling device and accurate measurement. It is a measuring tool approved by both parties of gas (oil) and gas (oil). It is convenient to check and replace the orifice plate without stopping the medium conveying, and the inspection and replacement of the orifice plate can be completed online within 3-5 minutes. The operation is flexible and easy, the sealing is reliable, safe and economical, the floor space is small, and the bypass pipeline is not needed. The calibrated measurement accuracy is less than grade 1.

It is widely used in power plant, chemical plant, oil field and natural gas pipeline transportation device.

Operating procedures for removing and installing orifice valve

Take out:
1. adjust the measurement in the metering room to the compensation state and stop the operation of relevant instruments.
2. open the balance valve of the valve body, balance the pressure of the upper and lower valve chambers, turn the spool shaft clockwise with special rocker, open the spool valve, and connect the upper and lower valve chambers.

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3. turn the orifice guide plate lifting shaft in the anti clockwise direction, lift the orifice guide plate to the valve chamber, then turn the spool shaft counterclockwise to close the spool valve.

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4. close the balance valve, open the vent valve of the upper valve body, and completely vent the natural gas in the upper valve body.
5. open the blowdown valve, remove the bottom dirt of the orifice valve, and close the drain valve after draining.
6. loosen the pressing screw shaft, put forward the pressing plate, take out the cover plate and gasket, turn the guide plate lifting shaft of the hole plate anticlockwise, and put forward the guide plate to the outside of the valve.

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7. take the orifice plate and rubber ring out of the guide plate, clean the guide plate, orifice plate with cleaning agent, and visually measure the quality of the orifice plate (if the quality is obviously defective or if other hole plates with other holes are required to be installed, take the orifice plate out of the guide plate and replace it). Then check the opening diameter with vernier caliper and make records, and check whether the sealing ring is damaged.

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1. Install the hole plate that is cleaned or needs to be replaced into the guide plate (pay attention to the right angle of the orifice plate aligned with the upstream air direction), put the guide plate vertically into the valve body, move the upper and lower guide plate lifting shaft to make the guide plate in position, and then shake the hole plate guide plate into the upper valve body.

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2. Install the sealing gasket, put the valve body cover plate vertically into the cover plate groove, install the pressure plate, and tighten the pressure plate bolts evenly.
3. Close the vent valve, open the balance valve, and check the leakage at each sealing place with soap water.
4. Turn the spool shaft clockwise to open the spool valve, shake the guide lift shaft clockwise, lower the guide plate to the working position of the lower valve body, turn the spool shaft anticlockwise to close the spool valve.

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5. Close balance valve, open vent valve, and close vent valve after discharge.
6. Rotate the gland of the valve body sealing grease box and inject the sealing grease (the sealing grease is used to seal the sealing surface of the valve valve).

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The function of the slide valve is to cut off the upper and lower cavities. The sealing grease is injected between the slide valve and the top plate of the slide valve to ensure the sealing between them.

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Installation conditions of orifice valve

(1) The straight pipe section before and after the throttling piece must be straight without visible bending.
(2) The straight pipe section for installing throttling element should be smooth. If it is not smooth, the flow coefficient should be multiplied by the roughness to correct the sparsity.
(3) In order to ensure the fully developed turbulent velocity distribution at 1D in front of the throttling element and make the distribution uniform and axisymmetric
1) The straight pipe section must be round, and the roundness requirements for the front 2D range of throttling parts are very strict, and there are certain roundness indexes. Specific measurement methods:

  • (A) On four vertical pipe sections OD, D / 2, D and 2D in front of throttling piece, at least four single measured values of pipe inner diameters shall be measured at approximately equal angular distance, and the average value D shall be taken. The difference between the single measured value and the average value of any inner diameter shall not exceed ± 0.3%;
  • (B) After the throttling element, 8 single measured values of inner diameter are measured at od and 2D positions by the above method. Compared with D, the maximum deviation of any single measured value shall not exceed ± 2%.

2) A long enough straight pipe section is required before and after the throttling piece. The long enough straight pipe section is related to the form of the local resistance piece in front of the throttling piece and the diameter ratio β.
(4) The length of the straight pipe between the first and second resistance pieces on the upstream side of the throttle piece can be 1 / 2 of the listed value according to the form of the second resistance piece and β = 0.7 (no matter what the actual β value is).
(5) When the upstream side of the throttling element is an open space or a large vessel with a diameter ≥ 2D, the length of the straight pipe between the open space or the large vessel and the throttling element shall not be less than 30d (15d). If there are other local resistance parts between the throttling part and the open space or large vessel, the total length of the straight pipe section from the open space to the throttling part shall not be less than 30d (15d), except that the minimum length of straight pipe section 1 specified by the attachment is set between the throttling part and the local resistance part.

Maintenance of orifice valve

1. The surface of orifice valve shall be kept clean, the paint shall not fall off or rust, the name plate shall be clear, the parts shall be complete and intact, and the movable part shall be flexible and easy to use.
2. Check the operation of the orifice valve once a month, remove the dirt on the surface of the orifice, and visually inspect the important parts of the orifice. If there are scratches, corrosion pits, wear and other defects, they should be replaced. If the seal is damaged or deformed, it must be replaced. The inspection contents mainly include:

  • (1) Plate surface inspection (whether there is dirt on the surface of orifice plate; whether there is scratch; whether there is corrosion);
  • (2) Entrance edge inspection (whether there is obvious scratch on the entrance edge; whether there is burr on the entrance edge of cylindrical opening; whether there is damage on the entrance edge; whether there is deformation; if the upstream surface of orifice plate is inclined at an angle of 45 ° and sunlight or artificial light source is used to shoot at the entrance edge, it is qualified if there is no reflected light);
  • (3) Roughness inspection (check the roughness of orifice plate with the same material);
  • (4) Flatness inspection (check whether the orifice plate is flat).

3. Add sealing grease once a month.
4. Do not scratch or damage the surface of the orifice plate and the seal when disassembling the orifice plate. Do not use metal tools to remove the dirt on the orifice plate.
5. After lifting the orifice plate, if crystal precipitation is found on the surface of the orifice plate, the blowdown valve must be opened for blowdown.
6. When installing the orifice plate each time, clean the slot of the guide plate first, and then add proper amount of butter on the slot.
7. If it is found that the slide valve is not closed tightly, add sealing grease and move the slide valve to check its sealing condition and keep good sealing.
8. If the sealing of the slide valve is not good, open the upper valve cover and clean the sliding block and valve seat sealing grease of the slide valve. The dry and hard sealing grease can be dissolved and cleaned with alcohol.

Source: Network Arrangement – China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.ugsteelmill.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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