476
Issue date: 17 November 2006
25 of 80
14.14
The basic features of the standard valves are;
(a)
Brass/chrome plated valve body.
(b)
Flame retardant cylinder hand wheel - (incorporating ratchet mechanism).
(c)
Sintered filter element.
Ratchet hand wheel
14.15
The valve is fitted with a spring loaded ratchet hand wheel mechanism and is opened anti
clockwise; however during rotation of the hand wheel it will lift up (approximately 2mm) over the
ratchet mechanism, away from the valve body, and then rapidly down due to the compression
spring, riding over the ratchet mechanism.
14.16
A ‘click’ will be heard as the hand wheel moves down. This will occur six times per revolution, i.e.
every 60°.
14.17
The ratchet mechanism is designed to prevent inadvertent closing of the valve when in use.
14.18
To close the valve it is necessary therefore to manually lift the hand wheel (against the spring
force) away from the valve body and over the ratchet mechanism, at the same time rotate the
hand wheel clockwise to close the valve. This action may have to be repeated to achieve final
closure.
Ratchet valve
14.19
When the valve is in the ‘closed’ position, the sealing face of the lower spindle seals onto the
sealing rim of the valve body, preventing high pressure air from being discharged from the
cylinder.
14.20
Turning the hand wheel of the valve anti clockwise (looking at the top of the hand-wheel) rotates
both the spindle and the threaded lower spindle opening the valve.
14.21
As the lower spindle rotates in the threaded bore it moves away from the sealing rim of the valve
body and along the square drive of the spindle.
14.22
The released high pressure air from the cylinder discharges to the compressed air breathing
apparatus attached to the valve outlet.
14.23
To ensure no restriction of air to the breathing apparatus, and to maximise the airflow from the
cylinder, the valve should always be fully opened.
14.24
During opening, the hand wheel will be felt to lift up and down the ratchet mechanism.
14.25
Continue to turn anti-clockwise until a resistance is felt, indicating that the valve is fully open.
14.26
Do not force any further. When the resistance is felt, turn the hand wheel in the opposite
direction (clockwise) to engage the first ratchet this will take much less than 60° of a rotation.
14.27
Engaging the first ratchet will ensure that no movement to ’close’ the valve can occur without
having to lift the hand wheel over the ratchet.
14.28
To close the valve pull the hand wheel away from the valve body to lift and override the ratchet
mechanism, and rotate (clockwise).
14.29
Repeated pulling and clockwise rotation of the hand wheel rotates the spindle and threaded valve
head.
