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Model 3900 Liquid Level Controller Model 3900
Liquid Level Controller
zMallard Control Company, Inc. 2004; All Rights Reserved
07/04
The Model 3900 Liquid Level Switch is a pneumatic snap
acting or electric SPDT or DPDT High/Low level switch.
This rugged instrument applies the same "Force Balance"
control mechanism as the Model 3200 Liquid Level
Controller, combined with a compact vertical cage
assembly. The Model 3900 is designed specifically to
meet the level control requirements found on onshore
and offshore oil and gas production equipment.
Features:
Electric or Pneumatic - The Model 3900 Liquid
Level Switch can be fitted with either a non-bleeding
pneumatic snap (on/off) pilot or a SPDT or DPDT
electric switch.
Field Reversible Switch Action - Changing switch
action requires no special tools and no additional
parts, and can be easily done without removing the
instrument from the vessel. Refer to the Switch Action
section on Page 2.
Field Reversible Mounting - Simply follow the instructions
provided on the inside of the instrument's cover. Again, no
special tools and no additional parts are required.
Marine Service - The Model 3900 Liquid Level Switch
comes standard with stainless steel internals for marine
type environments.
NACE - The Model 3900 Liquid Level Switch can be made
to meet NACE MR-01-75 material specifications for sour
service. Specifications
Process Connection
Threaded:
1" FNPT
Flanged
1
:
2"
Butt Weld
1
:
1", 1.5", and 2"
Socket Weld
1
:
1"
Displacer Cage Pressure Rating
2
FNPT, BW, SW:
2250 psig (155 bar)
Flanged:

150# RF
275 psig (19 bar) 300# RF
740 psig (51 bar) 600# RF
1480 psig (102 bar) 600# RTJ
1480 psig (102 bar) 900# RF
2220 psig (152 bar) 900# RTJ
2220 psig (152 bar)
Temperature Limit
-20 to 400°F (-29 to 204°C)
Switch Type
Pneumatic Snap Pilot (On/Off), standard
Electric SPDT, optional (rated Class I, Group B/C/D, Div. 1)
Electric DPDT, optional (rated Class I, Group B/C/D, Div. 1)
Minimum Allowable Fluid Specific Gravity
Snap Pilot:
0.50
SPDT Switch:
0.50
DPDT Switch:
0.75
Supply Pressure Requirements (Pneumatic Pilot)
0-20 psig output: 25 psig supply
0-30 psig output: 35 psig supply
Electric Switch Rating
SPDT:
15A @ 125, 250, or 480 VAC
DPDT:
10A @ 125 or 250 VAC
Supply & Output Connections
Pneumatic Pilot: 1/4" FNPT
Electric Switch:
1/2" FNPT (Conduit Connection)
Materials of Construction
Level Switch:
Case / Cover:
Anodized Die-Cast Aluminum
Snap Pilot:
Anodized Aluminum with
Aluminum Seat and SST Internals
Gauges:
Bronze Internals (standard)
316 SST Internals (optional)
316 SST, Liquid-Filled (optional)
Brass Internals, Liquid-Filled (optional)
Cage / Body Assembly:
Cage:
WCC Steel
Body:
1018 Steel
Displacer:
316 SST (standard)
Alloy 20 (optional for NACE)
Displacer Arm:
304 SST
Seals:
Viton (standard)
Buna-N (optional)
Switch Action
Action refers to the change in instrument output that results
from a change in instrument input. The input is the liquid level,
which is detected through the mechanical force applied to the
instrument linkage from the relative weight of the displacer.
The output is the "making" or "breaking" of a circuit. A reverse
acting level switch is one that "breaks" a circuit on rising level.
A direct acting level switch is one that "makes" a circuit on
rising level.
The Model 3900 Liquid Level Switch is available in either
direct or reverse acting configurations. For switches equipped
with the pneumatic snap pilot, "making" the pneumatic circuit
means connecting supply air to the output port in order to
pressurize a signal-receiving device. "Breaking" the pneumatic
circuit is done by connecting the exhaust port to the output
port to remove pressure from the signal-receiving device.
Changing the switch action is done by moving the Flapper Bar
pivot point to the opposite side of the switch housing. This is
easily performed in the field and requires no special tools.
For switches equipped with electric SPDT or DPDT pilots,
"making" the electrical circuit means closing the electrical
contacts, while "breaking" the circuit means opening the elec-
trical contacts. The switch is supplied with three leadwires
per set of contacts - "C" (common), "NO" (normally open),
and "NC" (normally closed) - and a ground leadwire. A direct
acting switch (contacts to close on rising level) is achieved by
using "C" and "NO" wires. A reverse acting switch (contacts
to open on rising level) is achieved by using "C" and "NC"
wires.
IMPORTANT NOTE: Moving the Flapper Bar pivot point is
not necessary to change switch action for electrical switches.
All Model 3900 switches with electric pilots are shipped from
the factory conforming to the above wiring requirements. If
the Flapper Bar pivot point is reversed, the action of the
switch contacts will be reversed.
1. Top / bottom connections only.
2. Maximum pressure ratings at 100°F (38°C).
Page 2 Page 3
Connection Type
Process Connection
1
1.5
2
Lbs
(Kg)
Lbs
(Kg)
Lbs
(Kg)
FNPT
47
(21)
-
-
-
-
Butt Weld
1
-
-
-
-
47
(21)
Socket Weld
1
47
(21)
-
-
-
-
150# RF
1
52
(23)
54
(25)
59
(27)
300# RF
1
55
(25)
59
(27)
63
(29)
600# RF
1
55
(25)
63
(29)
67
(31)
600# RTJ
1
55
(25)
63
(29)
67
(31)
900# RF
1
64
(29)
81
(37)
95
(43)
900# RTJ
1
64
(29)
81
(37)
95
(43)
Approximate Shipping Weight, Pounds (Kg)
1. Top / bottom connections only.
Dimensions:
MODEL 3900
WITH ELECTRIC PILOT Mallard Control Company, Inc.
4970 Washington Boulevard
Beaumont, Texas, USA 77707
409 842-5392 Phone
409 842-8165 FAX
www.MallardControl.com
While this information is presented in good faith and believed to be accurate, Mallard Control Company does not guarantee results based upon such information.
Mallard Control Company reserves the right to change the design or specifications of these products without notice.
Sample Model Number: 3900 - 10 FS - S V RD - S M
Model Number Information
MOUNTING ORIENTATION / SWITCH ACTION
CODE
Left Hand / Direct (Open Pneumatic Pilot on Rising Level)
LD
Left Hand / Reverse (Open Pneumatic Pilot on Falling Level)
LR
Left Hand / Electric Pilot
LE
Right Hand / Direct (Open Pneumatic Pilot on Rising Level)
RD
Right Hand / Reverse (Open Pneumatic Pilot on Falling Level)
RR
Right Hand / Electric Pilot
RE
CASE
CODE
Marine Service
M
Marine Service with Piped Exhaust
N
SEAL MATERIAL
CODE
Viton (standard)
V
Buna-N
B
Special
(specify)
PILOT
CODE
Pneumatic Snap
S
Electric SPDT, Explosion-Proof
E
Electric DPDT, Explosion-Proof
D
PROCESS CONNECTION SIZE
CODE
1
10
1.5
15
2
20
PROCESS CONNECTION STYLE
CODE
FNPT (Screwed)
FS
Socket Weld
SW
Butt Weld, Sch. 40
B4
Butt Weld, Sch. 80
B8
Butt Weld, Sch. 160
B1
Flanged
RF
RJ
ANSI 150
F1
J1
ANSI 300
F3
J3
ANSI 600
F6
J6
ANSI 900
F9
J9
ANSI CLASS (PRESSURE RATING)
CODE
Cage / Body
Displacer
Shaft/Blk Brng
WCC Steel
316 SST
303 SST
-
WCC Steel
316 SST
316 SST
A
WCC Steel
(NACE)
Alloy 20
316 SST
N
SUPPLY / OUTPUT GAUGES
CODE
Standard Service
S
316 SST
6
Brass, Liquid-Filled
B
316 SST, Liquid-Filled
D
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