Issue/Rev. 0.4 (6/17) ║ MN03010 • Page 5
2 – Operation
2.1 Principle
The Smith Meter
®
Model 210 Valve (Figure 1) fundamentally consists of a Smith
Meter
®
200 Series Valve with two solenoid controls. A valve response control device,
typically a needle valve, is located between each solenoid and its respective up-
stream or downstream port. This device is used to fine tune the opening/closing rates
of the valve, as well as provide control loop isolation for easier control loop service.
Adjustment of these devices controls the flow rate to and from the cover chamber
permitting valve adjustments based on product viscosity and pressures.
N.O.
Solenoid
(30B)
N.C.
Solenoid
(30A)
Opening
Speed
Control
Closing
Speed
Control
Flow
Strainer
The normally open (N.O.) and normally closed (N.C.) solenoids, located in the
upstream and downstream portions of the control loop, respectively, control the
operation of the valve. When both solenoids are energized, high upstream pressure
is blocked from reaching the main valve cover, the pressure in the cover vents to
downstream (lower pressure), and the valve opens. Conversely, when both solenoids
are deenergized, the downstream control loop is blocked and high upstream pressure
closes the valve.
During flow, when the N.O. solenoid is energized while the N.C. solenoid is
deenergized, pressure is trapped in the cover causing the valve poppet to be
hydraulically locked in a fixed open position. Therefore, a constant flow rate is
maintained. When operating conditions change causing a change in flow rate for that
fixed valve opening, the flow controller (e.g., microLoad, or AccuLoad) signals the
appropriate solenoid to open or close momentarily, changing the valve open position,
thereby readjusting the flow rate to its set value.
When the set flow rate changes (e.g., from low flow start to high flow limit, or
during multi-step valve shutdown), the appropriate solenoids are signalled to open
and/or close until the flow rate adjusts to the new set value. When the product
delivered reaches a predetermined (field adjustable first stage trip) value in the
controller, valve closure is initiated. The flow controller signals the 210 Valve to ramp
down the flow in a multi-step manner, thus preventing line shock.
Model 210 Valve (I / O / S) Manual
Operation
Figure 1
– Model 210 Valve Schematic
