Emerson Daniel 788DVC User Manual page 12

Introduction
October 2019
CAUTION
EQUIPMENT DAMAGE
Read the entire recommended procedure for all installation operations and
maintenance procedures before attempting to install or disassemble the valve.
Disassembly of this cylinder assembly is different from previous Daniel Control Valves
and requires strict adherence to the procedures outlined in this manual.
Failure to read and comply with these procedures could result in damage to the
equipment and compromise in the integrity of the operation.
1.2.3 Operation overview of the control valve
The Model 788DVC Series Control Valve operates on a balanced-piston principle. When
pressure on both sides of the piston are equalized, a spring located on top of the piston
acts as a differential force and closes the piston. When the pressure against the bottom of
the piston exceeds the pressure plus the force of the spring exerted against the top of the
piston, spring tension is overcome, and the valve opens. See
information.
These valves are normally closed (N.C.) and they will open when both solenoids are
energized. The valves are fail-safe as they close upon loss of power. They use the line
product as the source of hydraulic power to open and close the main valve piston. An
electrical supply controlled by an electronic preset is the source of power for energizing
the two solenoids.
These valves are used mainly for batching and they provide a means of reducing the rate of
flow on on startup and before final shut-off of a predetermined delivery. This minimizes
surges of pressure and line shock and ensures ± 1/4 gallon shut-off (sizes 2 inch - 8 inch) of
the preset volume.
The total system generally consists of three pieces of equipment: (1) a flow meter, (2) an
electronic preset with digital control, and (3) a digital electric control valve. The electronic
preset is the device used to set the predetermined volume of liquid that is to be delivered
by the valve.
Operational sequence
With both solenoids de-energized, the main valve is closed as shown in
main valve can be infinitely positioned anywhere between 0 - 100% open by digital control
of the solenoids. With both solenoids energized, as shown in
to open. It will only open to the programmed flow rate set in the electronic preset.
Normally, the electronic preset is programmed to digitally control low flow startup,
maximum flow rate, low flow rate before shut-off and no flow. The electronic preset will
automatically energize and de-energize the solenoids to position the main valve to limit
the required flow rate. When the required flow rate is reached, the solenoids will be as
shown in
increase, the valve will close slightly to adjust to the required flow rate. All of the
positioning is done by digitally controlling the two solenoids as shown in
1-2 and
12
Figure 1-2. This hydraulically locks the main valve piston in position. Should flow
Figure 1-3.
User manual
P/N 3-9008-556
Figure 1-1 for more
Figure 1-1. The
Figure 1-2, the valve begins
Figure 1-1, Figure
Model 788DVC Digital Control Valve