pg. 6
CHECK BACK FEATURE
When using liquid cylinders, it is not uncommon for the primary side pressure to drop below the switchover
point even if there is still a significant amount of gas left in the cylinder. This could be caused by an increase in
downstream demand during peak gas usage, or, when the liquid volume in the cylinder becomes low.
As a result, manifold systems without a Check Back feature may do one of two things –
1. Switch to the reserve side until the pressure builds back up and then switch back to the former primary
side. This will happen repeatedly resulting in both sides of the manifold being depleted at the same time,
or,
2. Switch to the reserve side permanently resulting in a significant amount of gas left in the cylinder
unused.
To avoid either of these situations, the Model 763 DataSmart manifold has an electronically controlled Check
Back feature that performs as follows:
a) If the primary side pressure goes down below the switchover point, the system temporarily switches
over to the reserve side. The system does not go into alarm mode at this point and the system
status does not change.
b) The LCD screen indicates “Check Back” mode.
c) After 30 minutes, the system checks back to see if reserve side pressure has recovered to 15% or
more above the switchover point
d) If so, the system switches back and uses gas until the switchover pressure is reached
e) If not, the system goes into alarm mode and shows empty
f) The DataSmart system will perform steps a, b and c three times. After that, the system goes into
alarm mode and switches over to the reserve side. System status lights will change at this time.
g) After the system goes into alarm mode, any increase in pressure 15% above the switchover point
on the empty side resets the check back feature and assumes the empty cylinder has been
replaced.
ECONOMIZER FUNCTION
Liquid cylinders that are in reserve with no gas being used will continue to build head pressure until the relief
valve opens venting gas to the atmosphere where it is lost and cannot be used. The Model 763 DataSmart is
constantly sensing pressure being built up on the reserve side. If the reserve side pressure builds up to within
85% of the relief valve setting, the system will switch over to the reserve side for 5 minutes to use gas and
lower the building head pressure before the relief valve activates. The DataSmart system will continue to
sense increasing pressure on the reserve side and activate in 5 minute intervals so long as a liquid dewar is
installed on the reserve side. This is also indicated on the LCD screen as a function of the “Check Back”
feature.
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