Wafer Check Valve Installation, Operation and Maintenance Manual

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1. Introduction
The design of this type of check valve has good structures and appearance. The discs open under the flow pressure with direction from inlet port to outlet port. When the inlet pressure is lower than outlet pressure, the discs close automatically due to differential pressure and weight of the discs as a result of preventing backflow. The valve is designed according to API 594 with face to face as per ASME B16.10 and the pipeline flange to ASME B16.5, the pressure test of this type valve is according to API 598. This type of valve is widely used in industries like petroleum, water, natural gas etc. as well as power plant, metallurgy and textile industries.

2. Purposes
This type of valve is widely used in petrochemical ad general industrial pipelines for preventing pumps and other power driven machine from reversing, as well as releasing mediums in the machines.

3.Design Features
» Discs can automatically close with the effects of springs, fast in closing as to keep the medium from backflowing.
» The valve can be installed horizontally and it is light so that supporting seat is not necessarily required.
» Discs can fully open with a little differential pressure, fast speed and good sealing performance.
» Flow coefficient is 2.6 to 0.7, it becomes smaller as the valve size is larger.
» Short face to face, small volume and light weight saves material, therefore reduces the cost.
» The valve is one-piece type, simple and compact with low water hammer effect, the life span of this valve is long and it is reliable.

4. Installation
» Before installation, check the body cavity if it is clean and no dirt of other corrosive residue, remove dirt and clean the valve, repair the defects which are caused during the transportation.
» When installing the valve, verify the operating requirements are in accordance with that marked on body and nameplate. Check if the model of the valve, flange size and face to face length is suitable for the application pressure and temperature.
» Dual plate check valve is normally installed horizontally in vertical or horizontal pipelines.
» Pay special attention to the flow direction when installing the valve, the flow direction shall be the same as the arrow marked on valve body, otherwise the valve will cut the flow required.
» When the check valve is closing, the water hammer pressure will emerge. It will be too serious to cause damage to the valve , pipeline or equipment, specially for big size or high pressure pipelines. Users shall pay highly attention to valve selections. »After installation, clean the pipeline with clean water, remove possible residue during the installation in order to protect the sealing surface from being scratched.

5. Installing Pipeline Flanges
A pre-tightening force shall be applied when installing the valve to realize sealing. In addition, if the valve is not aligned to the pipe centerline and increase pre-tightening
force of the bolts to realize sealing, it will increase the gasket load and pressure load to the valve, as a result, there will be leakage between the connections.
» Inspect the flange matching face, if defects that can cause leakage are found (e.g. deeper groove caused by retracting, dents caused by mis-operation), it shall be removed and repaired before it can be installed.
» Check the size, length and material of the bolts and nuts conform to the operating requirements;
» Material and size of the gasket shall conform to ASME B16.5;
» Check if the gasket is capable of anti-injurious defects or damages.
» Check carefully when installing the matching flanges for its correct alignment.
Apply some lubricant to the threads of bolts, equally fasten the bolts during the assembly, make sure the initial contact of flange and gasket is smooth and parallel. The bolts shall be symmetrically and equally fastened, try not twisting the two flanges, especially when it is installed to existing pipelines of which parallelism of flanges is critical.

6. Repairs
» If leakage is found between the seating surfaces, first check the seating surface for residue or other greasy substances, clean the seating surface with clean oil waste dipped with some detergent.
» If the seating surfaces are pinched, grind the upper and lower seating surfaces with 800# sandpaper.
» When leakage is excessive, the valve shall be dismantled, grind the disc and seat seating surfaces, replace when necessary.