Pipelines & Pipeline Safety - 'SHAFER' AUTOMATIC LINE-BREAK VALVE
Written by Norrie
Thursday, 29 April 2010 19:53
Page 8 of 12
'SHAFER' AUTOMATIC LINE-BREAK VALVE
'Shafer' Line Break Valves are fitted at intervals along the length of a particularly long pipeline.
The function of these valves, is to close automatically in the event of a 'Line-break' (rupture of the pipeline). Should such an event occur, the Shafer valves will 'sense' the large, sustained pressure drop in the affected section of pipe. Two valves will trip 'closed' and isolate the section involved.
Following is a description of the operation of a 'Shafer' valve - please refer to the diagrams together with the notes.
FIGURE: 8 -NORMAL OPERATING 'OPEN' POSITION
In this diagram, all systems are at normal operating conditions. Small, short-lived pressure fluctuations - up to about 30 Psi, (passage of spheres or compressor trips etc..), will not affect the Shafer valve. The valve control systems will remain equalized with the valve in the 'OPEN' normal operating position.
The parts of the system are:
- G.1. - Power gas cylinder.
- G.2. - Pipeline gas cylinder.
- H.1. - 'Closing' hydraulic oil cylinder.
- H.2. - 'Opening' hydraulic oil cylinder.
- D. - Diaphragm.
- R.O. -Adjustable orifice - The setting of this orifice determines the closing of the Shafer valve - (Psi Pressure drop/minute).
- P.1. and P.2. - Double poppet valves.
- V.1. and V.2. - Hydraulic oil transfer 'Latch' valves.
- V.3. - Pipeline gas to Power gas cylinder 'G.1.'
- V.4. - Pipeline gas to gas cylinder 'G.2.'
- V.5. - Check valve (to maintain maximum pressure in Power gas cylinder).
- C.P. - Shafer valve operating cylinder and piston
- L. -Control arm (lever) - For manual re-opening of the valve (or to check valve operation).
- M. - Manual operated hydraulic pump.
The power storage tank G.1. contains gas at the highest pressure the pipeline reaches. The spring loaded check valve V.5 allows higher pressure into tank G.1. (through shuttle valve V.3.), but will not allow Power Gas pressure to fall when pipeline pressure decreases.
Gas tank G.2 also contains gas at pipeline pressure, but this can change as line pressure fluctuates. The gas line from tank G.2 contains the adjustable orifice RO , and is connected to the pipeline (upstream and downstream sides of the Shafer valve) through shuttle valve V.4., which is centralized.
Each side of orifice - 'RO', a tapping is taken to the top and bottom of Diaphragm 'D'. The diaphragm is spring-loaded to hold it 'DOWN' during normal operation.
The rate of pressure drop and time delay to valve closure is set by the adjustment of the restriction orifice 'RO'.
In conjunction with the diaphragm, a control arm 'L' and double-poppet valves P.1. & P.2. activate the Power gas system from tank G.1 to the top of the two hydraulic tanks H.1. and H.2.
With the Shafer in the fully open or fully closed position the control arm is horizontal and all pressures in the system are stabilized.
Tanks H.1 and H.2. contain hydraulic oil for the activation of the Shafer valve operating piston - 'CP'.
The oil from tank H.1. feeds the 'Closing' (top) side of the valve operator piston, while the oil from tank H.2. feeds the 'Opening' (under) side of the piston.
While the Shafer is fully open (or fully closed), the two hydraulic tanks are open to atmosphere through the two poppet valves P.1 and P.2.
Connected into the hydraulic oil systems, two piston operated latch valves V.1. and V.2. operate to stabilize the hydraulic system when the valve is fully closed or fully open.
In the hydraulic oil system, a hand operated hydraulic pump 'M' is installed for manual operation to open the valve when no gas pressure is available - as after a prolonged shut-down - and has an 'OPEN - NEUTRAL - CLOSE' selector.
Last Updated on Thursday, 29 April 2010 19:56