Schuck valve analysis and maintenance

1 SCHUCK Valve Body Analysis

1.1 Schuck ball valve housings are different from common ball valve housing welding methods SCHUCK ball valve uses two semi-circular wrought steel shells to be welded on the bearing surface with only one weld, which is consistent with the shape of the sphere with a small number of external tolerances. The valve body consists of two semi-circular forged steel shells welded on the bearing surface with only one vertical weld. The vertical weld is in parallel with the sealing seat of the valve. It avoids the two-way valve when the valve body is welded to the housing. Block soft seal material damage at high temperatures.

1.2 all welded ball valve;

SCHUCK valve uses forged valve body and ball body. It is a true all-welded structure. No part of the valve body is connected to the body of the valve body by bolts or pins. Therefore, all potential leakage routes are eliminated, and the best safety is achieved. performance.

1.3 The ball valve is a fixed ball. Its support ring system can be self-centered and floated. It has a pre-tensioned spring element. The ball is positioned by the pin, and the sealing force automatically increases with the pressure of the pipe.

1.4 The valve stem is designed to prevent explosion;

The overall structure of the valve stem and ball, the ball valve requires only a very low torque when opening and closing, its seal and bearing is maintenance-free and maintenance-free, under the maximum working pressure of the pipeline, the journal seal can be replaced without interrupting the pipeline work.

2 SCHUCK valve stem, seat seal analysis

2.1 The stem is sealed with a 3-stage seal and has a fire protection function;

The three-stage sealing device consists of the first stage being pre-stressed by the spring, the second stage is composed of upper and lower isolation rings and the fireproof seal in the middle, and the third stage is composed of an O-ring and bolts capable of further tightening. The three-stage seal guarantees the tightness and fire protection of the stem from the bottom up. By increasing the preload of the spring, the seal ring can be further pressed, the driving force of the seal ring can be increased to prevent leakage, and the U-shaped main seal ring can be replaced with pressure during the grease injection.

2.2 Double seats The double-piston seat uses a PMSS seal, which is a metal-to-metal seal, and the seal assists the use of additional textured rubber for sealing. This kind of valve seal has the characteristics of wear resistance, non-deposition, and dirtiness, and may reach "0" leakage.

The use of a drop-type seal groove design increases the sealing performance of the ball valve, in particular, prolongs the service life of the seal.

2.3 Valve body accessories and function analysis Ball valve has a sewage pipe and an empty pipe, which can eliminate pipe dirt, can eliminate excessive pressure inside the ball cavity or automatically discharge excessive pressure inside the pipe, increase the sealing of the ball valve, and test Ball valve is completely sealed and has anti-static function.

Upstream and downstream of the ball valve, there is a gas supply line to supply gas to the actuator cylinders. There are two ball valves on each side of the pipeline. In normal working conditions, only the pipeline on the upstream side should be opened to supply gas to the cylinder.

The valve has a double cut-off and discharge (DBB) function, and the ball valve can achieve a double shut-off band discharge function in both of the switches. When the valve is closed, downstream of the valve can safely perform pipeline maintenance and other operations. Shuke's all-welded valve does not require any pressure balancing holes on the service ball, and it also has a DBB function at the valve opening position. It is convenient to check the effectiveness of the valve seat seal. The cavity of the valve body can be depressurized, and each side can withstand the full pressure difference. The valve body and the valve seat support cooperate with the surface of the inner hole plated with PTFE.

2.4 Actuator Analysis The valve uses a gas-liquid linkage actuator to drive the valve stem. The valve stem rotates the ball between 90° to achieve the purpose of opening and closing the valve. The actuator adopts a fork-type drive method. The basic principle is that the control system controls the opening and closing of the solenoid valve and introduces the external air into the gas-liquid storage tank. The gas pushes the piston in the hydraulic cylinder with the hydraulic oil as the medium, and is connected to the piston. The connecting rod pushes the fork motion, and the fork is nested on the valve stem to drive the valve rod to act, so that the reciprocating action completes the switching of the valve. The implementing agency can achieve local, remote control and ESD capabilities.

2.5 Explosion protection system analysis The explosion protection system is essentially a small remote control terminal unit (RTU) that monitors the pressure change in the pipeline and automatically controls the valve closure. The main function is that the system controls the valve actuator to close the valve to prevent the tube burst event when the system continuously monitors the pressure change of the pipe and detects that the pressure change rate of the pipe reaches the set value or the pipe pressure exceeds the set value. Valve pressure drop value means that when there is a pipe burst accident, when the natural gas in the pipeline rapidly drops to a certain pressure value, the valve actuator valve can be quickly closed to ensure that there is no large amount of natural gas leakage, thereby avoiding major accidents. A kind of protection. The choice of pipeline pressure drop value is to avoid the accidental closure of the valve caused by the start and stop of the compressor, and to ensure that the valve responds quickly when there is a pipeline explosion. For example, the pressure drop of the electronic control unit (electronic burst protection device) of the valve is set to 5 bar/min. When the pressure drop in the pipeline is greater than or equal to this value, the ball valve will automatically close.

3 SCHUCK valve maintenance

(1) Routine maintenance.

1 Maintain the seat sealer grease system; 2 Fill the grease with the required amount of grease at low grease injection pressure; 3 Inspect the valve for signs of corrosion or paint, coating damage; 4 From fully open to fully closed position After the valve is fully opened and operated repeatedly, this step is repeated several times to evenly spread the sealing grease and ensure that the valve can be easily rotated. If you do not have full-cycle operating conditions, it is generally permissible to implement a half-cycle, that is, the valve body rotates 15 to 30°.

(2) Comprehensive maintenance.

1 Cleaner Clean old grease or sealant. After emptying, inject the cleaning agent, cycle the valve, so that the cleaning agent is spread on the sealing surface, and the cleaning agent can be left in the valve for 1 to 2 days; 2 the ball valve is in the closed position, and the valve body outlet opening or the vent opening is lowered. Valve chamber pressure; 3 Shut off the valve body drain outlet and vent, according to the required amount of injection detergent, repeat the cycle switch valve; 5 grease or sealant, cycle switch valve to ensure that the valve is flexible; 5 valve body vent, test valve Seat seals, if the seat still leaks, adjust the position of the ball; 6 After the adjustment of the position of the ball seat, the seat leakage still does not stop, and then inject the sealing grease again to test.