as fittings are called various devices and devices mounted on gas pipelines, apparatuses and devices, with the help of which they turn on, turn off, change the amount, pressure or direction of the gas flow, as well as remove gases.
Classification of gas fittings
According to their purpose, the existing types of gas fittings are subdivided:
- for shut-off valves – for periodic tight shutdowns of individual sections of the gas pipeline, equipment and instruments;
- safety valves – to prevent the possibility of gas pressure increase beyond the established limits;
- reverse acting fittings – to prevent gas movement in the opposite direction;
- emergency and shut-off valves – to automatically stop the movement of gas to the emergency section in case of violation of the preset mode.
When choosing gas equipment and fittings, it is necessary to be guided by the current GOST and SP.
Valuable information is contained in the materials of the Research and Development Center for Industrial Gas Equipment which collects, analyzes, and verifies the reliability of information on the quality, reliability, competitiveness and safety of industrial gas equipment products.
Shut-off valves include various devices designed for hermetic shutdown of individual sections of the gas pipeline. They must ensure tight shutdown, quick opening and closing, ease of maintenance and low hydraulic resistance. Gate valves, taps, valves are used as shut-off valves on gas pipelines.
The most common type of shut-off valves are gate valves (figure below), in which the gas flow or its complete cessation is controlled by changing the position of the valve along the sealing surfaces. This is achieved by rotating the hand wheel. The spindle can be retractable or non-retractable. When the hand wheel rotates, the non-extending spindle moves around its axis together with the hand wheel.
Depending on which way the flywheel rotates, the threaded bush of the valve moves along the thread on the lower part of the spindle down or up and, accordingly, lowers or raises the valve. Rising spindle gates move the spindle and associated gate valve by rotating a threaded bushing attached to the center of the flywheel.
For gas pipelines with pressures of up to 0.6 MPa, valves are made of gray cast iron, and for gas pipelines with pressures of more than 0.6 MPa, they are made of steel. Gate valves can be parallel and wedge. For parallel gates, the sealing surfaces are parallel, with a spacer wedge between them. During the installment any valve the gas fitter should be an expert in his skill who has got gas fitter course with on field experience.
a – parallel with the movable spindle: 1 – body; 2- locking discs; 3 – wedge; 4 – spindle; 5 – flywheel; 6 – stuffing box packing; 7 – housing sealing surfaces; b – wedge with a non-rising spindle: 1 – wedge; 2- cover; 3 – bushing; 4 – nut; J – flywheel; 6 – stuffing box; 7 – collar; 8 – spindle
When the valve is closed, the wedge rests against the bottom of the valve and pushes the discs, which, with their sealing surfaces, create the necessary density. In wedge gates, the side surfaces of the gate are not parallel, but oblique. Moreover, these valves can be with a solid shutter and a shutter consisting of two discs. It is advisable to install parallel valves on underground gas pipelines.
However, valves do not always provide a tight shut-off, as often the sealing surfaces and the bottom of the valve become dirty. In addition, during operation of valves with an incompletely open shutter, the discs wear out and become unusable.
All repaired and newly installed valves must be checked for tightness with kerosene. To do this, the valve should be set in a horizontal position and poured with kerosene on top, on the other side, the valve should be painted with chalk. If the valve is tight, there will be no kerosene stains on the valve.
On underground gas pipelines, valves are mounted in special wells (figure below) made of precast concrete or red brick. The overlap of the well should be removable for ease of disassembly during repair work.
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