Refrigeration system ammonia (fluorine) valve maintenance knowledge

‌ One, refrigeration system valve classification

Refrigeration system valves are common ammonia refrigerant valves, freon refrigerant valves: globe valves (including surface valves), throttle valves, check valves, solenoid valves, liquid level float valves, automatic bypass valves, safety valves, etc。

2. Body material and sealing surface

    The new series of ammonia system welding valves are generally cast steel welded structures, and the small ones are cast steel and cast iron structures。At the same time: the old series of valves are mostly made of cast iron, cast steel and stainless steel (rare according to the design requirements), and the sealing structure is mostly made of polytetrafluoroethylene。The nominal pressure is usually 2.5MPa。

    Three, how to correctly identify the valve

    (1) View the qualifications of the manufacturing unit: the manufacturing unit of the valve must obtain a special equipment (pressure pipeline components) manufacturing license in accordance with the requirements of the "Special Equipment Safety Supervision Regulations" and the "Pressure Pipeline Components Manufacturing Licensing Rules" before it can manufacture the corresponding valve products。The unit using the valve should purchase qualified products produced by the unit with manufacturing qualifications。(2) Check the random data of the valve: the certificate and nameplate of the valve, focus on checking whether the valve indicates the words "ammonia special valve", check whether the nominal pressure, use temperature, applicable media and other information of the valve are suitable for the use of the valve, especially pay attention to the lower limit of the applicable low temperature。Sometimes the valve applicable medium is not indicated, pay attention to the valve model in the sealing surface code, code B (babbitt) or F (polytetrafluoroethylene) can be used, if other avoid use, prohibit the use of copper sealing port (sealing surface code T) valve。(3) Check the valve body identification: ammonia valve handwheel paint yellow marks;Check the valve body nominal pressure (PN), nominal diameter (DN), valve body material identification such as WCB (carbon steel), LCB (low temperature carbon steel), CF (304), CF3 (304L), CF3M (316L), etc，See if there is a manufacturing license mark (TS)，See if there is a manufacturer and casting furnace lot number identification;Whether the above marks are consistent with the certificate information;(4) Identification of cast iron valves: In some cases due to the loss of relevant information can not identify the valve body material，If the valve is used in the case of high pressure and low temperature，It is easy to have a valve burst accident，Therefore, the body material identification work is very important。Identification method: ① appearance inspection，Cast iron is rough in appearance，Macroscopic defects such as sand holes, pores, slag holes and sand inclusions can be seen in appearance.② hardness check，General casting material hardness value is higher，Gray cast iron Brinell hardness is generally HB170~240, grade HT250 cast iron hardness is generally HB187~250, grade QT450 ductile cast iron hardness is generally HB160~210;(3) Spectral analysis of all elements，Pay attention to the carbon content，If the carbon content is greater than 2.06% is cast iron material。

Fourth, special attention in the installation and use of ammonia valves

    (1) The selection of the installation valve of the ammonia (fluorine) refrigeration system should be determined according to the requirements of the design document or the use condition (working pressure, working temperature, etc.)。

(2) Before installation, carefully check whether the mark is consistent with the use requirements;Check whether the packing is compressed, should ensure the sealing of the packing, but must not hinder the rotation or lifting of the valve stem;During installation, the dust and debris in the valve cavity and the pipeline should be eliminated so as not to affect the sealing performance, and the screw thread part of the valve stem should be kept lubricated during operation。Ensure that the valve is installed in the same direction as indicated on the valve body or required。Flange connection bolts should be fully assembled。

(3) Installation specifications include SBJ12-2000 "Ammonia Refrigeration System Installation and Acceptance Code" and GB50274-98 "Refrigeration equipment, air separation equipment installation engineering construction and acceptance Code"。GB 50274-1998 "Refrigeration equipment, air separation equipment installation engineering construction and acceptance code" No. 2.5.11 Valves on the lubrication system and refrigerant pipelines shall meet the following requirements: valves with good sealing performance for inlet and outlet, certified and installed within the guarantee period，Only the sealing surface can be cleaned;For valves that do not meet the above conditions，Disassemble and clean，The packing and gasket should be replaced according to the requirements of the valve。SBJ 12-2000 "Ammonia refrigeration system installation engineering construction and acceptance Code" No. 3.1.2 stipulate that only the sealing surface can be cleaned for valves used in ammonia refrigeration systems and related lubricating oil systems with good inlet and outlet sealing performance and within their warranty period;Valves that do not meet the conditions should be disassembled, cleaned, and the packing and gasket should be replaced according to the relevant requirements of the valve。In fact, the two refer to a problem, the emphasis is on cleaning the sealing surface, because the connection between the ammonia special valve and the blue plate is a concave and convex surface, so it is required to clean it to prevent foreign bodies from causing a lax seal。

(4) All valves of the ammonia (fluorine) system should also be reversed to close the valve seat, so that when the valve packing leaks, the valve can be fully opened and the packing can be replaced when the system is in working condition and under certain pressure。

(5) There is now a seamless steel pipe integral stamping valve, which is specially used in refrigeration systems。

(6) Low-temperature occasions should use low-temperature LCB alloy steel valves or stainless steel valves, can not use ordinary WCB valves。

(7) In the synthetic ammonia system, the high pressure part is generally used with high pressure Angle globe valves, and the low pressure part is used with ordinary globe valves。

(8) Liquid ammonia valve flange is concave and convex surface seal, sealing gasket with stainless steel/graphite winding pad。

(9) Each valve should be a single air tightness test，Valves and their accessories should be installed: one-way valves should be installed in accordance with the direction of refrigerant flow;Valve with handle，Handle not downward，Solenoid valve, thermal expansion valve, lift check valve and other valve heads should be installed vertically;The thermal expansion valve is installed near the evaporator，For adjustment and overhaul。

(10) In use, test paper and hydrochloric acid gas can be used to check the sealing of the valve flange and its packing;Pay attention to valve body deformation, bulging, leakage, cracks and other abnormal conditions，Check the damage of the insulation layer of the low-temperature valve，Do not hit the valve with metal，Check the static crossover of the valve，And test the jumper resistance and meet the standard requirements。

(11) When filling refrigerant into the container, the opening speed of the valve should be slow, so as not to cause brittle damage to the container and valve;Do not close the liquid refrigerant pipe and the valves at both ends of the device。To prevent liquid explosion from cracking the valve;When you open the return valve，It should also be done slowly，And pay attention to the sound of refrigerant flow，Do not open suddenly，To prevent wet gas from rushing into the compressor，Cause an accident;When opening the valve，To prevent the spool from being stuck by the valve body，The handwheel should not be turned with excessive force，When the valve is fully opened, turn the hand wheel about 1/8 turns。Other operating matters Execute the relevant operating procedures。

(12) The use and installation unit to protect the technical data of the valve，These data are archived together with pressure pipe, pressure vessel and equipment related data，Facilitate the management of valve inspection and maintenance;The relevant units strictly implement the provisions of national laws and regulations, technical specifications and technical standards concerning valves，The user unit shall establish and improve the relevant systems of valve procurement, use, overhaul, inspection, test and scrapping, and formulate valve safety operating procedures;Operation and maintenance personnel should be strict with the corresponding system and procedures;The use of units to do regular inspection, overhaul, maintenance，And keep records。