What Do I Need To Know Before Purchasing A Valve

Sep 06, 2025

Valves are control components in fluid transport systems, with functions such as shut-off, regulation, diversion, prevention of backflow, stabilization, diversion, or overflow pressure relief. Valves used in fluid control systems have a wide variety of varieties and specifications, from the simplest globe valves to various valves used in extremely complex self-control systems. Valves can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metals, and radioactive media. Valves are also divided into cast iron valves, cast steel valves, stainless steel valves, chromium molybdenum steel valves, chromium molybdenum vanadium steel valves, duplex steel valves, plastic valves, non-standard customized valve materials, etc.

What technical requirements should be emphasized when purchasing valves

1, The specifications and categories of valves should comply with the requirements of the pipeline design documents

1. The model of the valve should indicate the national standard number requirements it is based on. If it is an enterprise standard, the relevant description of the model should be indicated.

2. The working pressure of the valve should be ≥ the working pressure of the pipeline. Without affecting the price, the working pressure that the valve can withstand should be greater than the actual working pressure of the pipeline; Either side of the valve should be able to withstand 1.1 times the valve working pressure without leakage when the valve is closed; When the valve is open, the valve body should be able to withstand twice the working pressure of the valve

3. The valve manufacturing standard should specify the national standard number it is based on. If it is an enterprise standard, the procurement contract should be accompanied by the enterprise document

2, Choose the material of the valve

1. Valve material, as gray cast iron pipes are gradually not recommended, the valve body material should be mainly ductile iron, and the brand and actual physical and chemical testing data of the casting should be indicated.

2. The valve stem material should strive for stainless steel stem (2CR13), and large-diameter valves should also have stainless steel embedded stem.

3. Nut material, made of cast aluminum brass or cast aluminum bronze, with hardness and strength greater than the valve stem

4. The material of the valve stem liner should have a hardness and strength not greater than that of the valve stem, and should not form electrochemical corrosion with the valve stem and valve body when immersed in water.

5. Material of sealing surface
① The types of valves vary, and the requirements for sealing methods and materials are also different;
② The material, fixing method, and grinding method of the copper ring for ordinary wedge gate valves should be specified;
③ Physical, chemical, and hygiene testing data for soft sealed gate valves and valve plate lining materials;

④ Butterfly valves should indicate the sealing surface material on the valve body and the sealing surface material on the butterfly plate; Their physical and chemical test data, especially the sanitary requirements, anti-aging performance and wear resistance of rubber; Usually, nitrile rubber and EPDM rubber are used, and the use of recycled rubber is strictly prohibited.

6. Valve shaft packing

① Due to the infrequent opening and closing of valves in the pipeline network, it is required that the packing should remain inactive for several years and not age, and maintain its sealing effect for a long time;

② The valve shaft packing should also have good sealing performance when subjected to frequent opening and closing;

③ In view of the above requirements, the valve shaft packing should be kept unchanged for life or more than ten years;

④ If the packing needs to be replaced, the valve design should consider measures to replace it under water pressure conditions.

3, Transmission gearbox

1. The material of the box and the requirements for internal and external anti-corrosion are consistent with the principles of the valve body.

2. The box should have sealing measures and be able to withstand immersion in a 3-meter water column after assembly.

3. The adjustment nut of the opening and closing limit device on the box should be inside the box.

4. The transmission structure is designed reasonably, which can only drive the valve shaft to rotate during opening and closing, without causing it to move up and down. The transmission components are moderately engaged, and there is no separation slip during load opening and closing.

5. The gearbox and valve shaft seal cannot be connected as a leak free whole.

6. There are no impurities inside the box, and the gear meshing area should be protected with lubricating grease.

4, Valve operating mechanism

1. The opening and closing direction of the valve during operation should always be clockwise.

2. Due to the frequent manual opening and closing of valves in the pipeline network, the opening and closing speed should not be too high, even for large-diameter valves, it should be within 200-600 revolutions.

3. For the convenience of one person's opening and closing operation, the maximum opening and closing torque under pipeline pressure conditions should be 240m-m.

4. The valve opening and closing operation end should be square tenon, standardized in size, and facing the ground, so that people can directly operate it from the ground. Valves with discs are not suitable for underground pipelines.

5. Display panel for valve opening and closing degree

① The scale line for the degree of valve opening and closing should be cast on the gearbox cover or the outer shell of the display panel after changing direction, all facing the ground. The scale line should be brushed with fluorescent powder to indicate visibility; ② The material of the indicator disk needle can be stainless steel plate under good management, otherwise it is painted steel plate and aluminum sheet should not be used for production; ③ The indicator pin should be conspicuous and securely fixed. Once the opening and closing adjustment is accurate, it should be locked with rivets.

6. If the valve is buried deep and the distance between the operating mechanism and the display panel and the ground is ≥ 15m, an extension rod facility should be installed and firmly fixed for people to observe and operate from the ground. That is to say, the opening and closing of valves in the pipeline network is not suitable for underground operations.

5, Performance testing of valves

1. When mass manufacturing a certain specification of valve, authoritative institutions should be commissioned to conduct the following performance tests:
① The opening and closing torque of the valve under working pressure conditions;
② Under working pressure conditions, the continuous opening and closing times that can ensure the valve is tightly closed;
③ Detection of flow resistance coefficient of valves under pipeline water delivery conditions.

2. Valves should undergo the following tests before leaving the factory:
① When the valve is in the open position, the valve body should withstand an internal pressure test of twice the valve working pressure value;
② When the valve is closed, both sides can withstand 11 times the valve working pressure without leakage; But for metal sealed butterfly valves, the leakage value should not exceed the relevant requirements

6, Internal and external anti-corrosion of valves

1. The inside and outside of the valve body (including the gearbox) should first be shot blasted, sandblasted, and rust removed, striving for electrostatic spraying of powder non-toxic epoxy resin with a thickness of 0? 3mm or more. When it is difficult to electrostatically spray non-toxic epoxy resin on extra large valves, similar non-toxic epoxy paint should also be brushed or sprayed.

2. The interior of the valve body and various parts of the valve plate require comprehensive anti-corrosion measures. On the one hand, immersion in water will not corrode, and there will be no electrochemical corrosion between the two metals; Smooth surface on both sides reduces water resistance.

3. The hygiene requirements for anti-corrosion epoxy resin or paint inside the valve body should be accompanied by testing reports from relevant authoritative authorities. The chemical and physical properties should also meet relevant requirements.

7, Valve packaging and transportation

1. Lightweight blocking plates should be installed on both sides of the valve for secure sealing.

2. Small and medium-sized valves should be tied with grass ropes and transported in containers.

3. Large caliber valves are also packaged with simple wooden frame fixation to prevent damage during transportation

8, Check the factory manual of the valve

1. Valves are equipment, and the following relevant data should be indicated in the factory manual: valve specifications; model; working pressure; Manufacturing standards; Valve body material;; Valve stem material; Sealing material; Valve shaft packing material; Material of valve stem shaft sleeve; Internal and external anti-corrosion materials; Operation startup direction; revolutions; Opening and closing torque under working pressure conditions;

2. Manufacturer's name; date of production; Factory number: weight; The control dimensions for the overall length, width, and height of the connecting flange, including the aperture, number of holes, and center hole spacing, shall be indicated in a graphical manner; Effective opening and closing times; Valve flow resistance coefficient; Relevant data of valve factory inspection and precautions for installation and maintenance.