Illustration 1 illustration 2 illustration 3 – Dwyer HFO User Manual
Page 2
Operation:
Illustration 1 shows the primary mechanism for
a single flow alarm. The HFO dual-switch flow
alarms contain two sets of these same
components (wiring to the DIN connector is
described on page 3). The configuration is such
that the high alarm is for increasing flow, and the
low alarm is for decreasing flow.
The follower moves in unison with an orifice
plate inside of the unit’s pressure vessel via a
magnetic coupling in order to indicate flow rate.
As the follower moves with changes in flow rate,
the flow rate is determined by relating the
position of the flow indicator line to the
increments on the flow rate scale.
The pointer indicates the set point for the alarm
switch. In Illustration 1, the switch will be
actuated at all flow rates below 4 GPM. To
change the set point, simply loosen the switch
glide screw one (1) turn and slide the switch to
the desired position along the flow rate scale.
When the pointer is pointing to the desired flow
rate, re-tighten the switch glide screw.
Switches:
The switch is a simulated roller, lever operated
low force microswitch. The specifications for this
switch are listed on the first page. The switch is
actuated when movement of the follower
causes the switch lever to be lifted. In Illustration
2, the switch has not yet been actuated, and the
electrical circuit is through the normally closed
(NC) contact. Illustration 3 shows the switch
after it has been actuated. In this scenario, the
electrical circuit is through the normally open
(NO) contact.
4
4
4
4
2
2
2
2
6
6
6
6
8
8
1
10
0
8
8
1
10
0
G
G P
P M
M
POINTER
S
S W
W IIT
T C
C H
H G
G L
L IID
DE
E
S
S C
C R
R E
E W
W
F
F L
L O
O W
W R
R A
A T
T E
E
S
S C
C A
A L
L E
E
A
A L
L A
A R
R M
M
S
S W
W IIT
T C
C H
H
F
F L
L O
O W
W IIN
ND
DIIC
C A
A T
T O
OR
R
L
L IIN
NE
E
F
F O
OL
L L
L O
O W
W E
E R
R
Illustration 1
Illustration 2
Illustration 3