JFD B44771, Operation And Maintenance Manual, Page: 33 / 136

OM131 21
P1939-OM-131 R11 Chapter 2
Fig 2.5 shows the spool valve in another cross-section through the two-stage regulator. This
illustrates the position of the pull ring (Fig 2.5, Item 17) on the spool (Fig 2.5, Item 14). The spool
valve is moved from the closed to the open position by pulling the actuation cable. A bullet on the
end of the cable contacts the two ball bearings (Fig 2.5, Item 36) in the centre of the spool, drawing
the valve to the open position. The ball bearings then drop out of the way allowing the bullet to pass
through and away up the cable sheaths.
Gas flow’s from the regulator first stage to the spool (Fig 2.5, Item 14). When the SLS System is in
its stand-by mode, the spool isolates the first stage from the second stage of the regulator. When the
actuation cable is pulled, the spool moves across allowing gas flow to the regulator second stage.
The second stage of the regulator is a diaphragm type. The pin (Fig 2.4, Item 16) is held off the seat
(Fig 2.4, Item 13) by the diaphragm (Fig 2.4, Item 31) and the support plate (Fig 2.4, Item 11) under
the action of the spring (Fig 2.4, Item 19). As the pressure in the space to the right of the diaphragm
increases, the diaphragm and hence the pin moves to the left, sealing off the seat fully at the pre-set
outlet pressure.
The outlet pressure is adjusted by varying the tension of the spring (Fig 2.4, Item 19) by slackening
the locknut (Fig 2.4, Item 22) and adjusting the grub screw (Fig 2.4, Item 23) until the desired outlet
pressure is achieved.
2.3.5 Injection orifice
The injection orifice (Fig 4.4, Item 3) is shown in cross-section in Fig 2.6. It contains a group of
orifices in series with the flow path making many 90
o
changes in flow direction. The combined effect
is to allow the system to contain much larger holes than there would be for a single orifice with the
same resistance. This therefore reduces greatly the chance of blockage.
Fig 2.6 Injection orifice
2.3.6 Single stage regulator
Fig 2.7 shows a cross-section through the single stage regulator.