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4.5 The Gas Head & Main Valve
4.5.1 Removal & Dismantling
Referring to DIAG 5 and DIAG 6, use the following procedure to
dismantle the Gas Head and Main Valve Assembly, when necessary:
Remove the Gas Head (V) and Valve as a unit, by unscrewing the 2 Gas
Head Fixing Screws (A).
Slide the Front Wire Guide (B) from the Gas Head (V), discarding ‘O’
Rings if damaged.
To separate the Gas Head from the Valve, unscrew the Air Union (C) and
Oxygen Union (D) from the Valve and remove the Valve to Gas Head
Fixing Screws (E). Discard the Gasket (X).
Remove the four Diaphragm Housing Screws (G) (2 not shown), located at
the front face of the valve and separate the Diaphragm Housing (H) from
the Cam Spindle Housing (I).
Remove and discard the Valve Diaphragms (J).
Slide the Air, Oxygen, and Gas Plungers (K) including the Pilot Gas
Plunger (S) from the Cam Spindle Housing (I).
Gently extract the Valve Lever Plug (L) from the Cam Lever (M). Unscrew
the exposed Valve Lever Screw (N) and remove it. Remove the Washer
(O), Cam Lever (M) and Lever Return Spring (P), taking care not to lose
any of these parts.
WHEN & WHY?
The Gas Head and Main
Valve Assembly should
only be dismantled when it
is absolutely necessary.
For example:
When replacing the
Front Wire Guide.
When the Pistol
Valve needs
inspecting.
The Heat Shield
needs attention.
The Drive Box needs
repairing.
When changing Wire
Diameters.
If difficult to turn or in
case of Spindle
binding.
Gas leaking through
Valve.
Valve is sticking.
Periodically for
inspections (every 6
months).
After a flashback.
If gas flows are low.
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