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Selection valve to note
10-11-2013

Ball valve type selection

( 1) determine the nominal pressure, not with Pmax set to PN, but by temperature, pressure, material from the table to find the three conditions corresponding to the PN and PN valves meet the selected value .

( 2 ) determine the type of the control valve , the leakage to meet process requirements.

( 3 ) determine the valve type, the working pressure should be less than the allowable differential pressure valve , such as not, shall be considered from a particular point of view or select it valves.

( 4 ) temperature of the medium in the valve operating temperature range, ambient temperature meets the requirements.

( 5 ) According to the case considered unclean media attempts to prevent valve problems .

( 6 ) According to the chemical properties of the medium corrosion resistant valve consideration .

( 7 ) According to the medium pressure and containing a hard object , consider the valve erosion and abrasion problems .

( 8 ) consider the economic effects of comprehensive performance price ratio. Need to consider three questions:

a. structure is simple ( as simple as higher reliability ) , easy maintenance , spare parts are sources ;

b. lifetime ;

c. prices .

( 9 ) preferably order.

Butterfly - single-seat valve - seat valves - sleeve valve - angle valve - three-way valve - ball - eccentric rotary valve - diaphragm .

Choice of implementing agencies

( A ) The simplest is a pneumatic membrane , followed by piston , and finally electric .

( 2 ) electric actuator main advantage is the driving source ( mains ) convenient, but the price is high , reliability, water proof as pneumatic actuators , pneumatic therefore should be preferred .

( 3 ) the old bulky actuators , we have high reliability electronic fine small electric actuator available ( prices accordingly high ) .

( 4 ) old ZMA, ZMB diaphragm actuators can be eliminated by a lightweight multi-spring actuator generations ( performance improvement , weight, height decreased by about 30% ) .

( 5 ) piston actuator specification more varieties , old, big and stupid is no longer recommended selection , and use light new structure.

Material selection

( 1 ) Body pressure rating , temperature and corrosion resistance , etc. should not be less than the requirements of process connection pipes and styling products manufacturer should be preferred .

( 2 ) more water vapor or aqueous wet gases and explosive media , should not use cast iron valves.

( 3 ) when the ambient temperature is below -20 ℃ ( especially in the north ) , should not use cast iron valves.

( 4) cavitation, erosion more severe temperature and pressure of the medium constituting the rectangular coordinates , a temperature of 300 ℃, pressure is 1.5MPa area outside the two-dot chained , should be used for cutting the sealing surface wear-resistant materials , such as cobalt -based alloy or surfacing Division Terai alloy.

( 5 ) for corrosive media , the selection of corrosion resistant alloys must be based on the media type, concentration , temperature, pressure difference , select the appropriate corrosion-resistant materials .

( 6 ) body parts were treated with the throttle , throttle speed small body wall and allow a certain degree of corrosion, the corrosion rate can be lmm / years ; cutting pieces by high erosion, corrosion will bow [ increased leakage from large, the corrosion rate of less than 0.1mm / years.

( 7 ) of lining material ( rubber, plastic ) for selection of the working medium temperature, pressure and concentration must meet the use of the material , and the valve operation considering its physical and mechanical damage ( such as shear failure ) .

( 8 ) should not be optional vacuum valve body lined with rubber , plastic structure .

( 9 ) The two water treatment system shut-off valve should not use rubber lining materials .

( 10 ) The typical typical medium corrosion resistant alloy material options:

a. sulfuric acid : 316L, Hastelloy, Alloy 20 .

b. Nitric acid: aluminum , C4 steel , C6 steel .

c. Hydrochloric acid: Hastelloy B.

d. hydrofluoric acid : Monel .

e. acetic acid, formic acid : 316L, Hastelloy .

f. phosphate : Seoul due to Nickel , Hastelloy .

g. urea : 316L.

h. caustic soda : Monel .

i. Chlorine : Hastelloy C.

j. seawater : Due to Nickel Seoul , 316L.

( 11 ) By far the most versatile corrosion resistant material is PTFE, known as corrosion king. Therefore , you should first use an all PTFE valve corrosion ( Hualin the patented product ) , unusual circumstances ( such as temperature > 180 ℃, PN> 1.6) was selected alloys.

Select Edit flow characteristics provided below in this paragraph are preliminary selection, the choice of detailed specific information see :

(1) S> 0.6 when the election logarithmic characteristic .

( 2 ) a small opening , unbalanced force changes in the election of the large number of properties.

( 3 ) required parameters reflecting the speed is adjusted when the election straight , slow election logarithm.

( 4 ) Optional linear characteristic pressure regulation system .

( 5 ) Optional linear characteristic level regulation system .

Select the mode of action

( A ) under foreign common fault on or off to indicate that the failure to open , fault clearance, and China's open air , gas closed indicates just the opposite , the failure to open the corresponding gas valve closed , the corresponding fault off the gas valve open .

( 2 ) new light valves, fine small valve has not emphasize the positive effects of the implementation machinery , counterproductive , and therefore must be marked on the endnotes .

B ( gas closed ) K ( open air )

Spring range of options

( 1 ) The first is to choose spring range , but also to determine the scope of work of the spring .

( 2 ) to determine the scope of the work involved in calculating the output power of the spring to overcome the unbalanced force . If there are difficulties , should conditions ( mainly the differential pressure valve is closed ) to tell the manufacturer to help calculate and adjusted the spring and working range Factory ( Currently , many manufacturers simply do not do calculations ) .

Flow selection

( A ) in the orifice , the medium facing the direction of flow valve to open stream open to the direction of flow streams closed off .

( 2 ) Select the main flow control valve is a single sealed class , there are single-seat valves , angle type , single sealing sleeve valve three categories. It provides the base flow ( eg seat valve , V balls ) and arbitrary flow ( such as O balls ) .

( 3) When dg> 15 , the normally open stream selection , dg ≤ 15 when the small diameter valve , in particular an optional high flow valve closed , in order to improve life.

( 4 ) for the two optional flow switch valve closed .

( 5 ) If the flow of closed valve to oscillate , change over, open flow type can be removed.

Packing Selection

( 1 ) is commonly used valve V-shaped packing PTFE and graphite O- filler.

( 2 ) PTFE packing friction is small, but the temperature difference , short life ; graphite packing friction big , but the temperature , long life ; temperatures and with a valve positioner proposed election graphite packing .

( 3 ) If the PTFE packing often change , consider using graphite filler.

Select accessories

( A ) regulating valve accessories are: positioning , converters , following actuators, pressure valves, to secure his position valves, valves , filters, oil mist, trip switches, position transmitter , solenoid valves , hand wheel .

( 2 ) shall be complementary features and accessories to ensure the role of valve operation . Necessary is increased , does not increase unnecessarily . Unnecessarily increase the attachment will raise prices and reduce reliability.

( 3 ) The main function of the positioner is to improve the output force and velocity , do not need these functions , or without , not like with the locator .

( 4 ) for the rapid response system , not the valve moves fast , the optional converter.

( 5 ) strict proof occasions Optional: electrical converters + pneumatic positioner .

( 6 ) the solenoid valve should choose a reliable product , its action should not prevent action .

( 7 ) important occasions do not recommend hand wheel mechanism to prevent human malfunction.

( 8 ) is best provided by the manufacturer and the supplier of the valve assembly to ensure the reliability of systems and assemblies connected .

( 9 ) When ordering, should provide the name of the attachment , models, specifications , input signal and output signals.

( 10 ) to reiterate : Please note that the importance of these small things , especially reliability , if necessary, supporting Japan Waring House may pneumatic components such as solenoid valves .

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