The working principle of orifice flowmeter:
The standard orifice flowmeter is a typical differential pressure flowmeter. When the fluid flows through the orifice flowmeter, the stream will shrink at the orifice plate to make the area of the stream smaller, the flow velocity of the stream will increase, and the static pressure will decrease, and the differential pressure will be generated before and after the orifice. The greater the velocity of the fluid, the greater the differential pressure produced, so the flow rate of natural gas flowing through the orifice flowmeter can be calculated by measuring the differential pressure. This method of measuring flow is based on the law of conservation of energy and the equation of flow continuity. For example, the pressure difference signal before and after the throttle has the following relationship with flow 2: Flow 2 is proportional to the square root of differential pressure JP. Therefore, flow 0 is the differential pressure signal detected after the fluid flows through the orifice. It is measured that this is the measuring principle of the orifice flowmeter.
Composition of orifice flowmeter:
The natural gas flow measurement system is composed of a flow meter (or device) body for natural gas measurement, a secondary instrument (or detection compensation calculation device), and a natural gas component analysis system. The system is composed of measurement, calculation, analysis and integration equipment. Complete system 1"]. Among them, the most commonly used flow meters are orifice flow meters (or standard orifice flow meters) and positive displacement flow meters. At present, there are integrated orifice flow meters that allow advanced orifice valves and temperature Transmitter, differential pressure transmitter, pressure transmitter and flow totalizer are used for flow measurement. Compared with the original flow computer mode, there is no need to install a flow computer at the gas transmission and distribution station, but the integration The calculator is integrated with the relevant transmitter and installed on site. In order to ensure the accuracy of flow measurement and ensure that the fluid flow can achieve the full development of the speed distribution, the straight pipe sections before and after the orifice flowmeter are stipulated in accordance with relevant standards or industry specifications. Requirements.
Orifice plate throttling device:
The orifice plate, the orifice holder and the upstream and downstream measuring tubes constitute the orifice plate throttling device. The orifice plate is called a primary element, which is an important element that generates differential pressure. The perforated holes must be processed according to the specified requirements. The orifice plate is installed on the orifice plate holder, and the pressure-taking hole is also drilled on the orifice plate holder, and the differential signal guide tube is installed. The upstream and downstream measuring pipes refer to the upstream pipe section near the orifice 10D and the downstream 4D straight pipe section. Its composition is shown in Figure 2-1. It should be particularly noted that the measuring tube is only a part of the straight pipe section required for the downstream of the orifice plate. In the orifice flowmeter selection design, installation inspection, use and maintenance, the first thing to do is to follow the length of the straight pipe section on the downstream of the orifice plate required by the standard. Equipped with the rest.
When the orifice plate flowmeter leaves the factory, there should also be a section of pressure pipe, a straight-through shut-off valve and a flange connecting the upstream and downstream measuring pipes to ensure the installation of the orifice plate throttling device. In this way, the correct and accurate transmission of the differential pressure signal is ensured to meet the installation standards and user convenience.