Correct use of orifice valve must know a few things

What is a orifice fitting ?

The orifice valve is a novel flow metering and throttling device, which is suitable for the flow measurement of sulfur-containing or sulfur-free natural gas, oil, gas, water and other gases and liquids. It is widely used in energy, petroleum, chemical, metallurgical in the industry.

Structure diagram
Structure diagram

Working Principle

The orifice valve has a certain pressure. When the natural gas filled with the pipeline flows through the throttling piece (orifice plate) in the pipeline, the flow beam will form a local contraction at the throttling piece, so that the flow rate increases and the pressure decreases. The pressure difference is generated. The greater the flow rate, the greater the pressure difference generated. The smaller the flow rate, the smaller the pressure difference generated, so that the flow rate can be indirectly known.

working principle

Throttle element

Throttle element

The flow measurement method is based on the law of conservation of energy and the flow continuity equation. Its flow calculation formula is as follows:

How to install the orifice valve correctly?

  1.  The straight pipe section before and after the throttle must be straight, and there must be no visible bending.
  2. The straight pipe section used to install the throttle should be smooth. If it is not smooth, the flow coefficient should be multiplied by the roughness to correct the sparseness.
  3. In order to ensure that the flow of the fluid forms a fully developed turbulent velocity distribution at 1D before the throttling member, and make this distribution into a uniform axisymmetric shape, so:
    (1)、The straight pipe section must be round, and the roundness requirements for the front 2D range of the throttling part are very strict, and there is a certain roundness index. Specific measurement methods:
    (A) On the OD, D/2, D, 2D 4 vertical pipe sections before the throttling piece, measure at least 4 single measurement values of the inner diameter of the pipe at approximately equal angular distances, and take the average value D. The difference between the single measurement value of any inner diameter and the average value shall not exceed ±0.3%
    (B) After the throttling piece, use the above method to measure 8 single measurement values of the inner diameter at the OD and 2D positions, and compare any single measurement value with D, and the maximum deviation shall not exceed ±2%
    (2)、A long enough straight pipe section is required before and after the throttling piece. This long enough straight pipe section is related to the form of the local resistance piece before the throttling piece and the diameter ratio β.
  4. The length of the straight pipe section between the first resistance piece and the second resistance piece on the upstream side of the throttling piece can be in the form of the second resistance piece and β=0.7, (regardless of the actual β value), take 1/1 of the listed value 2
  5. When the upstream side of the throttle is an open space or a large container with a diameter of ≥2D, the straight pipe length between the open space or the large container and the throttle shall not be less than 30D (15D). If there are other local resistance parts between the throttling part and the open space or the large container, in addition to the specified minimum straight pipe length 1 between the throttling part and the local resistance part, from the open space to the throttling part The total length of the straight pipe section between the flow parts shall not be less than 30D (15D).

What are the performance characteristics of the orifice valve?

  1. The standard throttling parts are fully used, and have been recognized by the International Standards Organization. They can be put into use without real-flow calibration, and are also unique in the flowmeter;
  2. The structure is easy to copy, simple, firm, stable and reliable in performance, and low in price;
  3. 3: Wide range of applications, including all single-phase fluids (liquid, gas, steam), some mixed-phase flows, and products for pipe diameters and working conditions (temperature, pressure) in general production processes; 4: Detection parts and differential pressure display instruments It can be produced by different manufacturers, which is convenient for specialized scale production.

Operating procedures for taking out and loading the orifice valve into the orifice:

1. Take out

  1. Adjust the measurement in the measuring room to the compensation state, and stop the operation of the difference meter.
  2. Open the valve body balance valve, balance the pressure of the upper and lower valve chambers, turn the spool valve shaft clockwise with the special crank handle, open the spool valve, and connect the upper and lower valve chambers.
  3. Turn the orifice guide plate lifting shaft counterclockwise. Lift the orifice guide plate into the upper valve cavity, then turn the spool valve shaft counterclockwise to close the spool valve.
  4. Close the balance valve, open the upper valve body vent valve, and completely vent the natural gas in the upper valve body.
  5. Open the blowdown valve, remove the dirt at the bottom of the orifice valve, and close the blowdown valve after draining.
  6. Loosen the pressing screw shaft, lift out the pressing plate, take out the cover plate and the gasket, turn the orifice plate guide plate lifting shaft counterclockwise, and lift the guide plate out of the valve body.
  7. Take out the orifice plate and the rubber ring from the guide plate, clean the guide plate and the orifice plate with cleaning agent, visually check the quality of the orifice plate, and then use the vernier card to check the diameter of the opening and make a record, and check whether the sealing ring is damaged.

Install into:

  1. Put the orifice plate that has been cleaned or needs to be replaced into the guide plate (note that the right-angle edge of the orifice plate is aligned with the upstream air direction), put the guide plate vertically into the valve body, and move the upper valve body guide plate lifting shaft up and down to make the guide plate in the right position. Then rock the orifice guide into the upper body.
  2. Install the sealing gasket, put the valve body cover vertically into the cover groove, install the pressure plate, and evenly tighten the pressure plate bolts.
  3. Close the vent valve, open the balance valve, and use soapy water to test the leaks at each seal.
  4. Turn the spool valve shaft clockwise to open the spool valve, shake the guide plate lifting shaft clockwise, lower the guide plate to the working position of the lower valve body, turn the spool valve shaft counterclockwise, and close the spool valve.
  5. Close the balance valve, open the vent valve, and close the vent valve after draining.
  6. Rotate the gland of the sealing grease box of the valve body and inject the sealing grease (the sealing grease is to seal the sealing surface of the slide valve).

How to use the orifice valve correctly?

  1. The surface of the orifice valve should be kept clean, the paint should not fall off or corrode, the nameplate should be clear, the parts should be complete and intact, there should be no internal and external seepage, and the movable part should 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 defects such as scratches, pits, and wear, they should be replaced. If the seals are damaged and deformed, they must be replaced. The inspection contents mainly include:
    (1) Inspection of the board surface (whether the surface of the orifice plate is dirty; whether there are scratches; whether it is corroded)
    (2) Check the entrance edge (whether there are obvious scratches on the entrance edge; whether there is burr on the entrance edge of the cylindrical opening; whether there is any damage to the entrance edge; whether there is deformation; tilt the upstream surface of the orifice plate at an angle of 45°, and illuminate it with sunlight or artificial light sources. To the entrance edge, no reflected light is qualified)
    (3) Roughness inspection (contrast and check the roughness of the orifice plate with the orifice plate of the same material)
    (4) Flatness inspection (check whether the orifice plate is flat)
  3. Fill the sealing grease once a month.
  4. When disassembling and assembling the orifice plate, do not scratch or damage the orifice plate surface and seals, and it is forbidden to use metal tools to remove the orifice plate dirt.
  5. After the orifice plate is lifted, if there is crystal precipitation on the surface of the orifice plate, the blowdown valve must be opened for blowdown.
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