There are many types of valves and they are used in a wide range of applications. In the pipeline, sometimes it is the main equipment and plays a control role; sometimes it is a secondary equipment and plays an auxiliary role. If it is not used properly, there will be "running, dripping, leaking" phenomena, which will affect production if it is light, and cause accidents if it is serious. So understanding and using the valve correctly is a very important issue.
Butterfly valves are currently the most widely used and most diverse valves in heating systems.
Working principle: The valve disc is a disc, through the rotation of the valve stem, the valve disc rotates at 90°C within the range of the valve seat to realize the switch of the valve. It acts as a shut-off in the pipeline. Flow can also be adjusted.
Advantages: simple structure, light volume, convenient operation and good sealing.
Disadvantages: When fully open, the valve plate (sealing ring) is eroded by the medium. In heating engineering, the butterfly valves used include triple eccentric metal sealing butterfly valves and rubber soft sealing butterfly valves.
Triple eccentric metal seal butterfly valve
The so-called "triple eccentricity" refers to the offset of the relative position of the valve shaft and the valve plate in the valve. Ordinary butterfly valves have an eccentricity, that is, the centerline of the valve shaft deviates from the centerline of the sealing surface (the centerline of the valve plate); for high-performance valves, an eccentricity is added, that is, the centerline of the valve shaft deviates from the centerline of the valve (pipe centerline); The purpose of the double eccentricity is to make the sealing pair separate from each other after the valve plate is opened to 20°, thereby reducing friction (cam effect). On the basis of the double eccentricity mentioned above, the triple eccentricity butterfly valve adds another special eccentricity - the oblique cone, which is the offset of the valve plate (the sealing surface is inclined at an angle to the vertical surface of the pipe).In this way, within the 90° stroke range of the valve, the sealing pairs are completely separated, which not only strengthens the cam effect, but also eliminates friction; at the same time, when the valve is closed, when the sealing pairs are gradually closed, a "wedge effect" is generated, and the minimum torque achieve the tightest shutdown possible. The so-called "metal seal" means that the valve seat and sealing ring are made of wear-resistant, corrosion-resistant, and high-temperature-resistant alloys; at the same time, in order to avoid head-to-head contact between the sealing ring and the valve seat, the sealing pair is designed to be in flexible contact, that is, an "elastic metal seal" is formed. "Seal" to ensure tight closing and no friction when opening. With the "triple eccentric" structure and supplemented with "elastic metal seal", such valves are easy to operate, durable and well sealed. Triple-eccentric metal-sealed butterfly valves are generally used in the main line and main branch of the heating system. The caliber is above DN300. Imported triple-eccentric metal-sealed butterfly valves have no direction, but there are generally recommended installation directions, which should not be reversed; domestic ones have directionality, and generally the reverse direction is one leakage level or one to two pressure levels worse than the forward direction, and reverse installation is not allowed. If welding on a horizontal pipeline, the valve should be closed to protect the sealing ring; if welding on a vertical pipeline, the valve should be closed, and water should be poured on the valve plate to extinguish the welding slag when welding on the top. When installing on a horizontal pipeline, it is recommended that the valve stem be horizontal or have a certain inclination to the vertical direction to ensure the cleanliness of the bottom bearing.
Common problems in the use of valves
a) Keep the valve clean.
b) When lifting, the rope should not be tied to the hand wheel or valve stem.
c) Confirm that the valve is working properly before installation.
d) When welding, the ground wire of the welding machine must be placed on the steel pipe at the welding port on the same side to prevent the current from damaging the valve.
e) During the welding process of medium and small diameter valves, cooling measures should be taken for the valves.
f) Valves that are not frequently opened and closed in the pipeline should be rotated regularly.
In addition, there are problems of environmental corrosion and protection of valves, medium corrosion and protection of valves, temperature and pressure problems, sealing and leakage problems, etc. In short, although the valve is small, it has a lot of knowledge, which needs to be continuously learned and summarized by us.
The butterfly plate of the rubber soft seal butterfly valve is generally made of electroplated ductile iron, and the sealing ring is made of rubber material. Different sealing materials are used, and the performance is different. The commonly used ones are: butyl rubber, applicable temperature - 12°C - +82°C; ethylene propylene rubber, applicable temperature - 45°C - +135°C; heat-resistant ethylene propylene rubber, applicable temperature - 20°C - +150°C.
Commonly used in heating engineering are clip type (D371X) and flange type (D341X). DN125 and below can be driven by handle (D71, D41X). The wafer butterfly valve is small and light, quick to open and close, easy to operate, easy to install, easy to maintain, excellent in sealing and adjustment performance, and high in cost performance, so it should be vigorously adopted. The soft seal butterfly valve has no direction and can be installed arbitrarily. When the butterfly valve is in storage, the valve plate should be opened 4°-5°. In order to avoid deformation of the sealing ring under long-term pressure, affecting the sealing.