2.9
Terminal units
Adjustable AGS terminal unit
AGS terminal units incorporate a minimum of moving parts and are gas specific. Terminal units of similar
design are used in wall, pendant, trunking and hose boom installations and the principle of operation is the
same for all installations.
When a terminal unit is not in use, a spring loaded brass valve plug seats against the front body forming an
effective seal. Inserting the receiver unit probe and fully engaging the retaining screw thread unseats the brass
valve plug compressing the spring. Gas flow is through the central adjustable orifice and radial flutes within
the brass valve plug. Normally the flow rate through a terminal unit is controlled by the flow regulating valve
setting, however, the orifice provides a “choke” on reaching sonic flow conditions. In this situation the orifice
prevents any further increase in flow rates and limits the maximum flow rate to approximately 150 litres/min.
This provides an ultimate safety device to protect the patient and downstream equipment.
2.10 Duplex installation
Duplex installations consist of twin exhauster units, rated at 100 % of the maximum system demand, supplying
a common distribution system via non-return valves. Logic circuits within the control panel operate the
“Standby” exhauster unit in the event of the “Duty” exhauster unit failing. An adjustable system failure
pressure switch senses the vacuum level in the distribution system. This pressure switch is adjusted to - 70
mbar to operate when flow at the furthest terminal unit falls to 80 litres/min with a 4 kPa resistance to flow
(HTM02-01 - BS 6834). During periods of very high demand, this pressure switch operates logic circuits
within the control panel to activate the “Standby” exhauster unit in addition to the “Duty” exhauster unit,
restoring the vacuum and flow levels. A timer circuit ensures that the “Standby” exhauster unit operates for
15 minutes after the system pressure switch no longer senses peak demand.
Instruction book
21
Summary of Contents for AGS 1560
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Page 11: ...Simplified schematic of a AGS Simplex installation Instruction book 9...
Page 13: ...AGS Simplex AGS Duplex Instruction book 11...
Page 16: ...Service diagram AGS Simplex 1 ph typical Instruction book 14...
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