P.O. Box 40525 · Houston, Texas USA 77240-0525
Tel: 713·466·3552 · Fax: 713·896·7386
www.norriseal.com
1001-0113O — ©2013, January 2013
pilot thrust pin through the lever and
fulcrum.
By increasing tension on the spring,
a lower level is sensed. By decreas-
ing tension on the spring, a higher
level is required to produce the same
force as before.
Spring compression can be reduced
to a point where a hydrocarbon liq-
uid level will rise above the displacer
without transmitting enough force
to the pilot to produce an output. If
properly adjusted, water, with a
higher specific gravity, will rise to the
displacer resulting in a change in
weight of the displacer. This will
produce an output, thus sensing the
interface level of water and hydro-
carbon. This wide range of control
makes liquid interface sensing
possible.
P
ILOT
O
PERATION
As described in Principle of
Operation, force from the balance
spring is transmitted via the lever
and fulcrum to the thrust pin of the
pilot.
Snap, Relief, and Envirosave™Pilots
These pilots have
two seats. The upper
seat (D) is sealed by
a ball (A). On Snap
pilots (see Figure 4),
the ball seat is a
metal seat and on the
Relief and Envirosave
pilots, there is an
elastomeric
seat
ensuring zero-leak-
age seals. The upper
seat controls supply
air and the ball is
held in the closed
position by the supply air pressure.
When mechanical force upward
from the thrust pin (B) is sufficient
to overcome supply air pressure
holding the ball to the seat, the ball
snaps upward, supply air flows
downward and out the output port
(H), and the lower port is sealed by
the spherical end of the thrust pin
preventing supply air from escaping.
As the upward force on the thrust
pin is decreased to a point where
supply air pressure overcomes the
upward force, the ball once again
seals the supply air and simultane-
ously opens the lower exhaust port
venting gas from the control valve
actuator.
On the Relief pilot, the passage
between the supply air and the out-
put port is significantly larger per-
mitting supply air to exit the output
port at a faster rate.
Throttle Pilot
The Throttle pilot
(see Figure 5) also
has two seats to
admit supply gas
and exhaust “used”
gas. A diaphragm
(E) is used to sense
pressure/force feed-
back and a spring
assists closing pres-
sure on the thrust
pin.The
Throttle
pilot is operationally
similar to the Snap
pilot except that the output pressure
is proportional to the mechanical
force applied to the thrust pin (C). As
the thrust pin force changes, the pilot
seeks to maintain equilibrium by
either decreasing (exhausting) out-
put loading pressure or increasing
output loading pressure. Supply air
does not flow when the loading
pressures of the pilot are balanced.
Electric Pilot Switches
Two standard switches are available:
SPDT (Single Pole Double Throw)
and DPDT (Double Pole Double
Throw) in Splash-Proof, Explosion-
Proof, or Hermetically Sealed
configurations.
O
PERATING AND
M
AINTENANCE
M
ANUAL
Series 1001, 1001A, 1001XL Level Control
Page 4 of 12
Pilot
Sensitivity Fulcrum
Pivot Pin
Thumb Screw
Torque Bar
Level
Adjusting
Bar
Adjusting Knob
Snap Ring
Figure 3 — Reverse acting, left hand mount controller
Resorte de
equilibrio
Figure 4 —
Snap pilot
F
o
rc
e
Figure 5 —
Throttle pilot
F
o
rc
e