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How To Maintain The Accurate Performance Of A Steam Flow Meter
Jan 04, 2019

How to maintain the accurate performance of a steam flow meter

The accurate performance of the steam flow meter is one of the most concerned issues for customers, and everyone is very concerned about its use. We Huaheng Instrument has also accumulated a lot of experience in this issue, the most important one is concentrated in the following three aspects.

How to maintain the accurate performance of a steam flow meter

How to make a steam flow meter to maintain its accurate performance

1. Pay attention to the correct selection of steam flow meter

When choosing a steam flow meter, two factors should be considered.

    One is the range problem. The steam flow meter is not measuring properly, mainly due to incorrect range measurement during the selection. The steam consumption in the steam season is quite large, and the steam used in the steam season is very small. The difference in steam consumption is too great, and the flow range of the steam flow meter is difficult to adapt. The flow measurement range must be clarified, and on this basis, a steam flow meter that meets the relevant operating parameters can be selected to fully function.

    The second is the pipe diameter problem. When designing the throttling device, basically the nominal nominal pipe diameter value provided by the process is used. In fact, the nominal nominal pipe diameter value and the actual pipe diameter value are still in error, especially the coiled pipe, the nominal nominal pipe diameter value and the actual value sometimes The difference is still large, which causes the measurement error to increase, and the accuracy of the measurement is difficult to meet the design requirements. National standard: The diameter D of the pipe used to calculate the diameter ratio of the throttle should be the average of the inner diameter within 0.5D of the upstream of the upstream pressure port. The average of the inner diameters should be the average of the inner diameters measured in at least two cross sections of the vertical axis, and the value of the inner diameter (the inner diameter of the pipe used for the design) should be ±0.3%. It is best to measure the pipe diameter before design to reduce the calculation error.

How to maintain the accurate performance of a steam flow meter

2. Install the steam flow meter correctly

Any steam flow meter must be installed correctly, otherwise it will not work properly. For example, installing a steam meter near the steam outlet of a boiler, installing a steam meter near the shut-off valve or pipe elbow and at the lowest point of the pipe is an incorrect installation. To install the steam flow meter correctly, you need to do five things:

    1 There must be a long enough straight pipe section before and after the installed instrument.

    2 The steam meter cannot be installed at the lowest point of the whole casing road.

    3 The installation of the condenser must be highly valued. The two condensers must also be at the same level. The function of the two condensers is to condense the measured steam in the pressure guiding tube and to make the condensate surface in the positive and negative pressure guiding tubes have the same height and to maintain long-term stability; Condensate fluctuations cause errors in the measurement. The effective volume of the condenser should be greater than 3 times the maximum volume change of the working space of the differential pressure transmitter used. The cross-sectional area in the horizontal direction must not be less than the operation of the differential pressure transmitter. Area, the system ensures good sealing and no leakage; it is necessary to fully consider the convenience of maintenance, replacement and purging.

    4 The length of the pressure guiding tube is preferably within 16m, and the inner diameter is preferably Φ10-16mm to prevent clogging. The pressure guiding tube is insulated throughout the process and ensures that the positive and negative tubes are at the same temperature to avoid errors caused by density changes.

    5 The temperature measuring component is preferably placed outside the 10D downstream of the throttle. When the pressure is applied to the pipeline or the positive pressure pipe, if the pressure transmitter is installed under the throttle device, the pressure transmitter must be pipelined. The liquid column value is corrected to improve metering accuracy.

How to maintain the accurate performance of a steam flow meter

3. Strictly regulate the operation of the steam flow meter

(1) The instrument is put into operation. When the steam flow meter is put into operation, first close the positive and negative valves of the differential pressure transmitter, and open the valve slightly to check whether the valves and pressure guiding tubes are leaking. If there is no leakage, the first valve will be fully opened. Open the blowdown valve to discharge the sewage and let the steam discharge, then close the drain valve. Wait a while for the condenser and the pressure guiding tube to be filled with condensed water before starting normal operation.

    Proceed as follows:

    1 open the balancing valve;

    2 slowly open the negative pressure valve;

    3 then open the positive pressure valve;

    4 After a short pause, close the positive and negative valves at the same time; the differential pressure transmitter adjusts the static pressure error after the fourth step, and must be carried out when the liquid level in the condenser is consistently balanced, otherwise the liquid column will be static. Pressure error

    5 then open the positive and negative valves;

    6 Close the balancing valve and the meter starts. Note that when filling the positive and negative chambers of the differential pressure transmitter, the venting screw on the container should be unscrewed to allow the gas to drain before filling.

How to maintain the accurate performance of a steam flow meter

(2) Operation of the instrument. After long-term operation, the pipe and the throttling device will change, such as scaling, wear and corrosion. The throttle is based on the shape and size of the structure to maintain the accuracy of the signal, any geometric size changes will bring errors to the measurement. The change in measurement error is not noticeable from the signal, so periodic inspection of the throttle is necessary. Due to the continuous production nature of the company, it is generally carried out in parallel with the overhaul. If the geometric size does not change much, you can continue to use it, but the design data should be corrected according to the measured data to ensure the accuracy of the measurement.

(3) Maintenance of the instrument. Since the instrument is in a high-temperature, high-pressure water vapor environment for a long time, it is easy to cause damage to the watch, rust, impurities, etc., so frequent maintenance and regular maintenance are required. For example, in the long-term operation of the LFIX split-rotor steam flowmeter, the graphite bearing is worn to cause the shaft to jump up; the frost is not paid attention to, the damping water is frozen, and the watch is frozen. In particular, the steam flowmeter should check whether the round surface of the opening of the orifice plate is rusted, whether there is any dirt attached, and it should be cleaned regularly, and the orifice plate with serious corrosion should be replaced. The vortex flow sensor should pay attention to check whether the triangular prism gap is blocked by debris, whether the detecting component is malfunctioning, etc.