First Flange connection
Flange connection is a valve body with flanges at both ends, corresponding to the flange on the pipeline, and installed in the pipeline by bolting the flange. Flange connection is the most used connection form in the valve. Flange has convex surface (RF), flat (FF), convex-concave surface (MF) and so on. According to the shape of the bonding surface can be divided into the following categories:
(1) smooth type: used for valves with low pressure. Processing is relatively convenient;
(2) Concave-convex type: higher working pressure, can use medium-hard washers;
(3) tongue and groove type: available plastic deformation of the gasket, in the corrosive medium is more widely used, the sealing effect is better;
(4) trapezoidal groove type: oval metal ring for the gasket, used in the working pressure ≥ 64 kg / cm2 of the valve, or high temperature valves;
(5) Lens type: the gasket is lens shape, made of metal. Used for high pressure valves with working pressure ≥ 100 kg / cm2, or high temperature valves;
(6) O-ring type: this is a newer form of flange connection, which was developed with the emergence of various rubber O-rings, which is more reliable than the general flat gasket in sealing effect.
Second Pair clamp connection
Valve installed in the middle of the two flanges, the valve body usually has positioning holes to facilitate the installation of positioning, with bolts directly to the valve and the two ends of the pipeline wear clamped together in the form of connection.
Third Welding connection
(1) Butt-welding connection: the ends of the valve body are processed into butt-welding bevels according to butt-welding welding requirements, corresponding to the pipe welding bevels, and fixed to the pipeline through welding.
(2) socket welding connection: the valve body ends are processed according to the socket welding requirements, and the pipe is connected by socket welding.
Fourth Threaded Connection
Threaded connection is a simple connection method, commonly used in small valves. The valve body is processed according to each thread standard, and there are two kinds of internal thread and external thread. There are two kinds of threads, internal and external, which correspond to the threads on the pipeline. Threaded connection is divided into two cases: (1) direct sealing: internal and external threads directly play a sealing role. In order to ensure that the connection does not leak, often filled with lead oil, thread flax and polytetrafluoroethylene raw material tape; of which polytetrafluoroethylene raw material tape, the use of the day to see a wide range; this material is very good corrosion resistance, sealing effect is excellent, easy to use and save, when disassembled, can be removed intact, because it is a layer of non-adhesive film, much superior than lead oil, thread flax.
(2) Indirect sealing: the force of thread tightening is transmitted to the washer between the two planes, allowing the washer to play a sealing role.
There are five major categories of commonly used threads: (1) metric common threads; (2) imperial common threads; (3) thread sealing pipe threads; (4) non-thread sealing pipe threads; and (5) U.S. standard pipe threads.
They are summarized as follows:
①International standard ISO228/1, DIN259, for internal and external parallel threads, code G or PF (BSP.F);
② German standard ISO7/1, DIN2999, BS21, for the outer teeth conical, internal parallel thread, code BSP.P or RP/PS;
③ British Standard ISO7/1, BS21, for internal and external conical threads, code PT or BSP.Tr or Rc;
④ American standard ANSI B21, internal and external conical threads, code NPT G (PF), RP (PS), Rc (PT) tooth angle are 55 °, NPT tooth angle of 60 ° BSP.F, BSP.P and BSP.Tr collectively referred to as BSP teeth.
U.S. standard pipe threads including five: general purpose tapered pipe thread NPT, pipe joints with straight pipe thread NPSC, guide rod connection with tapered pipe thread NPTR, mechanical connection with straight pipe thread NPSM (free with the mechanical connection) and NPSL (with a lock nut loose with the mechanical connection). They are non-threaded sealed pipe threads (N: American National Standard; P: pipe; T: tapered)
Fifth Ferrules connection
Ferrule connection, in our country in recent years only developed, its connection and sealing principle is that when tightening the nut, the ferrule is under pressure, so that its edge bites into the outer wall of the tube, the ferrule outside the taper and under pressure with the connector in the body of the taper close, and thus can reliably prevent leakage. Such as instrumentation valves. The advantages of this form of connection are: (1) small size, light weight, simple structure, easy to disassemble; (2) strong connection force, wide range of use, can withstand high pressure (1000 kg / cm2), high temperature (650 ℃) and shock vibration; (3) can choose a variety of materials, suitable for corrosion prevention; (4) processing precision requirements are not high; (5) easy to install at high altitude.
At present, the ferrule connection form, has been used in certain small-diameter valve products in China.
Sixth Clamp connection
This is a fast connection method, it only requires two bolts, suitable for frequent disassembly of low-pressure valves. Such as sanitary valves.
Seventh within the self-tightening connection
Above various connection forms, are the use of external forces to offset the medium pressure, to achieve the seal. The following is the use of medium pressure for self-tightening connection form. Its sealing ring installed in the cone, and the media to the side into a certain angle, the media pressure to the cone, and then transferred to the sealing ring, in a certain angle of the cone, resulting in two points of force, one with the center line of the valve body parallel to the outward, the other pressed to the inner wall of the valve body. This latter force is the self-tightening force. The greater the medium pressure, the greater the self-tightening force. So this connection form, suitable for high-pressure valves. It is more than the flange connection, to save a lot of material and labor, but also need a certain amount of pre-tensioning force, so that in the valve pressure is not high, the use of reliable. Valves made by utilizing the self-tightening sealing principle are generally high-pressure valves. Valve connection form there are many, for example, there is no need to dismantle the small valves, with the pipe welded together; there are non-metallic valves, the use of socket connection and so on. Valve users should be treated according to the specific circumstances.
