Control valve accessories, such as electrical converters, electric valve positioner, pneumatic amplifier, to secure his position, valves, etc., are all pneumatic
Element, therefore, on the quality of the source of gas control valve according to the instrument air purification (HG/T20510-2000)
OK o
A dew point temperature. The dew point of the the condensed steam temperature under a certain pressure. Using the dew point to restrict the moisture content of the gas source is the common method of engineering design. Instrument air moisture content to operate under pressure condensation control requirements, therefore, typically controls the dew-point temperature under the operating pressure should be low 10 ° C than at least the minimum temperature of the environment. For example, the air drier outlet pressure 0.7MPa, Setting the minimum temperature for a 15 ° C, the operating pressure of the dew point temperature of at least a 25 ° C. For example, the Shanghai region, atmospheric pressure dew point temperature for a 40 ° C. Figure 6-11 shows the relationship between atmospheric pressure dew point and operating pressure dew point.
2. Dust content. The outlet of the filter dust particle size not greater than 3μm, dust less than lmg/m3. Avoid breathing the human industrial dust and atmospheric dust, flammable, explosive, toxic and corrosive gases (or steam).
3 oil content. The filter outlet oil content of not more than 10mg/m3 [8ppm (W)]. Selection of oil-lubricated air compressor or directly with the process air compressor as instrument air, must be equipped with efficient degreasing, oil content in the compressed air control below the predetermined value, and with appropriate filtering, drying apparatus and spare tank.
Air pressure. Should be based on the final instrument gas requirements into account. General limit pressure range of 500 to 800kPa (G) and
300 to 500 kPa (G) two levels. Cylinder actuator is recommended 0.7MPa. The pressure upper limit value of the feeding pressure of the air source is mounted under the normal operating conditions. The specified pressure lower limit value of the minimum pressure of the gas supply sent below this specified value should be sound and light alarm as soon as possible.
(5) air consumption. By a single control valve steady-state air consumption the 2M3 (standard) / h, low-power locator steady-state air consumption
0.8 ~ 1.3m3 (standard) / h estimates. Switching valve according to the size of the cylinder and the operation frequency estimate of gas consumption control valve 3 to 5 times. Should pay attention to the instrument manual air consumption is the supply pressure 140kPa, 20 ° C state air consumption, gas consumption should be converted to the standard state, and should be added to the leakage coefficient of 0.1 to 0.3.
direct acting
solenoid valves
6 tank volume OK. Gas supply should be set in the gas tank of sufficient capacity, the volume is calculated as follows
V = QstPo / (P1 P2)
Of formula V in a tank volume, m3;
Qs stretch source means daily design capacity, m3 (standard) / min;
The P1's normal operating pressure, kPa (A);
P2 a minimum sent pressure, kPa (A);
t-atmospheric pressure, typically, Po = 101.33 kPa (A);
Hold Time, min, made by the process specific time the ships hold time 5 to u20min.
standard air cylinder
