Summary: This section talks focus on review and analyze the proper selection of control valve needs attention, according to regulating valve valve type, the implementing agencies, materials, flow characteristics, mode of action, spring range, flow packing, Annex 9 summarizes the adjustment in Valve Selection of experience and attention, for the regulating valve control valve selection of employees to understand the knowledge, improve the level of a larger selection of helpful, but limited to the author is limited, it is inevitable there are many deficiencies and problems, and welcome to readers criticized correction.
Valve Selection:
(1) Determine Nominal pressure, instead of Pmax to the set of PN, but by the temperature, pressure, material three conditions from the table to find the corresponding PN and to meet the selected valve of the PN values.
(2) to determine the valve type, the leakage rate to meet the technological requirements.
(3) to determine the valve type, its working pressure should be less than the permissible differential pressure valve, such as not, shall be elected from a particular perspective or it valve.
(4) medium temperature valve operating temperature range, the ambient temperature to meet the requirements.
(5) According to the medium is not clean, prevent the problem considered valve.
(6) According to the media to consider the chemical properties of corrosion resistant valves.
(7) According to media pressure, and with a hard object, given the erosion and wear-resistant valve problems.
(8) consider the overall economic effect of the performance, price. Need to consider three questions:
a. Structure is simple (as simple as higher reliability), easy maintenance, spare parts are sources;
b. Life;
c. Price.
(9) preferred order.
Butterfly - Single-seat valve - seat valve - Sleeve Valve - angular valve - three-way valve - Ball Valve - Eccentric Rotary Valve - Diaphragm Valve.
Implementing agency of the options:
(1) The simplest is the pneumatic membrane, followed by the piston, and finally electric.
(2) The main advantage of electric actuators is the driving source (power) to facilitate, but the high price, reliability, water-proof explosion-proof than pneumatic actuator, it should be preferred pneumatic.
(3) The old electric actuator cumbersome, we have refined a small high-reliability electronic Electric actuators available (prices accordingly high).
(4) The old ZMA, ZMB film enforcement bodies may be eliminated by the implementing agency on behalf of more than a light spring of the (performance, weight, height decreased by about 30%).
(5) Detroit Pistons executive body more varieties of different specifications, the old, big, stupid proposal no longer used, while the choice of the new structure of light.
Material choices:
(1) Body voltage levels, temperature and corrosion resistance, etc. should not be less than the technology requirements of connecting pipes, and preference should be given shape product manufacturer.
(2) Water vapor or water more wet gas and flammable and explosive media, should not use cast iron valve.
(3) when the ambient temperature is below -20 ℃ (especially the north), should not use cast iron valve.
(4) cavitation, erosion more severe temperature and pressure medium consisting of rectangular coordinates, its temperature is 300 ℃, pressure of 1.5MPa to connect two points outside the zone, the sealing surface on the throttle should be use wear-resistant material, such as cobalt-based alloy or the Secretary Terai surfacing alloy.
(5) pairs of strong corrosive medium, corrosion resistant alloy selection must be based on media type, concentration, temperature, pressure difference, choose a suitable corrosion-resistant materials.
(6) and the throttle body parts and treat them separately, the speed throttle valve wall of small and allow for a certain amount of corrosion, the corrosion rate can be lmm / years; savings have been brought to high-speed erosion, corrosion will bow [from leakage by large, the corrosion rate should be less than 0.1mm / year.
(7) on the lining materials (rubber, plastic) and a choice of the working media, temperature, pressure, concentration must meet the use of the material and consider it when the valve moves the physical, mechanical damage (such as shear failure) .
(8) Vacuum valves lining Body should not use rubber, plastic structure.
(9) Water Treatment System 2 shut-off valve should not use rubber lining.
(10) Typical corrosion resistant alloy materials typical of the medium options:
a. Sulfuric acid: 316L, Hastelloy alloy, 20 alloy.
b. Nitrate: Aluminum, C4 steel, C6 steel.
c. Hydrochloric acid: Hastelloy B.
d. Hydrofluoric acid: Monel.
e. Acetic acid, formic acid: 316L, Hastelloy.
f. Phosphoric Acid: Due to Fall nickel, Hastelloy.
g. Urea: 316L.
h. Caustic Soda: Monel.
i. Chlorine: Hastelloy C.
j. water: Due to nickel Seoul, 316L.
(11) So far, the most universal anti-corrosion material is PTFE, known as "corrosion King." Therefore, we should first use corrosion-resistant PTFE valve, in unusual circumstances (such as temperature> 180 ℃, PN> 1.6) was selected alloys.
Flow characteristics of choice:
Here is the initial choice, the choice of more specialized information, see:
(1) S> 0.6, when selecting the right number of features.
(2) Small opening work, unbalanced force changes in the election of the number of features is large.
(3) The request parameters have been adjusted to reflect the election, when a straight-line speed, slow time selecting the right number.
(4) Pressure-conditioning systems in a straight line features optional.
(5) a straight line features an optional liquid-conditioning systems.
Mode of selection:
(1) Foreign Common failure, open or closed to indicate that the failure to open, fault off, and China's air opening and closing said gas on the contrary, failure to open the corresponding gas-closing valve, fault off the corresponding gas valve to open.
(2) New light valves, precision valves are no longer small-scale implementation of the mechanical stress the positive role of reaction, and therefore must be marked on the end of injection.
B (gas closed) K (air to open)
Spring range of choices:
(1) First is to choose spring range, but also to determine the scope of the work of spring.
(2) to determine the scope of the work involved in calculating the output power of spring to overcome the unbalanced force. If difficulties, should be conditions (mainly the differential pressure valve is turned off) to tell manufacturers to help calculate and tune a good spring and scope of work the factory (at present, many manufacturers simply do not level).
The flow of choice:
(1) In cutting mouth, media, the direction of flow opposite the valve core to open stream open to the direction of flow streams closed off.
(2) the choice of the flow of the main control valve is a single sealed class, there are single-seat valve, angle valve, single-sleeve valve seals 3 major categories. It provides flow-based (such as two-seat valve, V ball) and any movement (such as the O ball).
(3) When dg> 15, it is usually selected streams open, when dg ≤ 15 of the small-caliber valve, in particular, an optional high-pressure flow valve closed in order to improve life expectancy.
(4) two optional flow-off valve closed.
(5) If the flow of closed-valve oscillation, changing over, open-flow type can be removed.
Filling choices:
(1) The regulating valve is commonly used PTFE "V"-shaped filler and graphite "O"-shaped filler.
(2) PTFE packing friction is small, but the temperature difference, life short; graphite packing friction, but the temperature is good, long life; high temperatures, and with a locator the proposed election of graphite valve packing.
(3) If the PTFE packing often change, you can consider the use of graphite packing.
Accessories choice:
(1) the annex to the main control valve are: positioning devices, switches, following the actuators, pressure valves, Paul position valve, valves, filters, oil mist device, limit switch, position the sender device, electromagnetic valve, Hand Wheel.
(2) Annex complementary capabilities and to ensure the role of valve operation. Necessary for increasing and unnecessary does not increase. When an unnecessary increase in the annex will raise prices and reduce reliability.
(3) Locator main function is to increase the output force and movement speed, do not need those features, from time zone, not with a locator like.
(4) rapid response system, do not move fast valve, optional converter.
(5) a strict proof occasion, optional: Electrical Converter + pneumatic positioner.
(6) The solenoid valve should be selected and reliable products to prevent the want it to move without action.
(7) important occasions suggested hands-wheel mechanism to prevent human malfunction.
(8) is best provided by the manufacturer and assembly in the valve on the supply, in order to ensure the reliability of the system and the assembly connected.
(9) order, the name of the attachment should be provided, models, specifications, input signal and output signals.
(10) would like to reiterate: Please note that these "little things" the importance, in particular the reliability, if necessary, may be supporting pneumatic components, such as the solenoid valve ball valve Trunnion Mounted Ball Valve Floating Ball Valve Top Entry Ball Valve ball valve V Type Ball Valve
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