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Internal valves

Fisher internal valves have gained wide field acceptance for use as primary shutoff valves, excess flow valves and back check 1
valves . Internal valves are installed in the inlets and outlets (liquid or vapor) of pressure vessels and in piping systems to control
the flow of LP-Gas and NH (anhydrous ammonia). The most frequent application is on bobtail and transport truck tanks, but 3
they may also be used on large stationary storage tanks and on in-line installations. The valves can be used in conjunction with
or without pumps and compressors.

Features & Benefits

• Perform functions of three different units: 1. Primary Shutoff, 2. Excess Flow and 3. Back Check.
• Effective leak resistance with TFE spring loaded packing.
• Complies with NFPA 58 requirements.
• Three closing systems: 1. Manual, 2. Cable or 3. Air.
• Built-in excess flow valve offers closure when flow exceeds the valve’s rated capacity or piping is sheared off at the valve.
• Fusible links or plugs melt at 212°F – 220°F (100° C - 104°C) and allow valve closure in the event of a fire at the valve.

Principle of Operation

The operational schematic below depicts threaded valves,
however flanged styles operate in the same manner. For
detailed information, refer to the instruction manual provided
with the valve

View #1
The valve is held closed permitting a tight seal by both tank
pressure and the valve’s closing spring

View #2
Moving the operating lever to approximately the mid-point in
its 70° travel allows the cam to place the rapid equalization
portion of the valve stem in the pilot opening. This permits
a larger amount of product to bleed downstream than if the
operating lever were moved into the full open position.

View #3
After a few seconds, when the tank and the downstream pressure
equalize, the excess flow spring pushes open the main poppet.
The operating lever is moved to the full open position to ready
the system for transfer operation. The pump or compressor
should not be engaged until the valve is fully opened.

View #4
During the transfer operation, a flow, or sufficient flow surge,
greater than the valve’s excess flow spring rating will force the
main poppet closed. A small amount of product will continue to
bleed through the downstream side, but much less than in View
#2. Should this occur, the operating lever should be moved to
the full closed position in View #1 and the steps repeated.


Threaded Internal Valves

Fisher offers the widest variety of threaded internal valves in the
industry. While their most frequent use is in the liquid and vapor
openings of bobtail and transport trucks, the valves can also be used
in stationary storage tanks, complying with NFPA 58 requirements.
Designed as primary shutoff valves, the units are designed with
several features that help control product discharge.

Steel and stainless steel constructions are standard throughout with
total stainless steel construction available. The valves have spring-
loaded TFE packing for an effective seal against leakage. Standard
® ® disc material is Nitrile, but TFE, Kalrez , Viton , EPDM, and Neoprene are available. (Note: TFE seats are not bubble tight.)

All Fisher internal valves are suitable for LP-Gas or NH service. 3
Special construction is available for other compressed gases. All of
Fisher’s threaded internal valves have a compact, one-piece body
design. They can be actuated manually, by cable control, or with an
air cylinder.

Type C407 (1 1/4” Body Size) – An excellent valve for vapor return
lines on bobtail trucks. Other applications include use as a main
valve on small capacity pumping systems, NH nurse tanks and in-3
line installations.

C400 Series (2” & 3” Body Sizes) – Only Fisher offers three
different body styles in 2 and 3” threaded sizes so that the best body
style can be selected for the particular application.
Type C427 (Straight-Through Body) – The most compact and
economical unit in the series, Type C427 has one bottom outlet. The
C427 can be used on bobtail, transport, stationary tank and in-line

Type C421 (Tee Body) – This unit is designed with two outlets,
bottom and side. The side outlet permits installing horizontal piping
immediately adjacent to the tank without the need for extra pipe
fittings. Either connection can be used for truck filling or withdrawal.
The C421 is used primarily on bobtails and transport trucks.

Type C402 (Strainer Body) – This valve has three side outlets and
an integral strainer for pump protection. The three outlets allow
convenient pump installation and also provide extra openings for
tank evacuation. Another use for the C402 is in bulk plants for
cylinder filling and truck loading from a single outlet.







Flanged valves provide a sturdy and compact means of directly
mounting a pump or piping connection. Special stud bolts,
weakened with a groove on the outside diameter, are furnished
with the valves to permit the pump or piping to shear off in the
event of an accident, leaving the valve intact. A built-in excess
flow valve reduces the chance of uncontrolled product discharge
when flow exceeds the rated flow capacity.
All flanged valves have an internal screen for pump protection that
can be easily removed if the valve is used primarily for filling the
tank. They also contain TFE packing to resist stub shaft leakage.
These valves can be activated manually, by cable control or by air
cylinder, see pages 31 and 32.
3” Flanged Sizes

Type C404-24 – A single-flange unit widely used on bobtail and
transport trucks for a compact means of direct pump connection
to the valve outlet. Another application for the C404-24 is on in-
line installations.

Type C403-24 – A double-flange unit designed for special bobtail
truck applications where the pump must be lowered to clear the
truck frame or other obstacles. A special shear section in the body
permits the lower section of the valve to shear off in the event of an
accident, leaving the critical shutoff parts within the tank.
4” Flanged Size
(Stainless Steel Construction)

Type C404-32 – Used widely on transport trucks and large storage
tanks, the 4” flanged unit comes standard with all stainless steel
construction for maximum protection against rust and corrosion.
For easy ?eld maintenance, the seat ring is field replaceable.

The C404-32 is the only internal valve that cannot be opened and
closed by the Type P650 cable control. Refer to page 31.
Factory installation of an air cylinder or manual operating handle
(with remote release mechanism) is available on the 4” flanged
valves. Refer to ordering information below.






Air Interlock Systems

An air interlock system can be configured for transport and bobtail
trucks with air brakes by using air cylinder actuated internal
valves. This system simultaneously interlocks the internal
operation with the truck air brakes without affecting normal air
brake operation. It complies with DOT MC331 and NFPA 58
requirements regarding thermal and remote release feasibility.

The air interlock system permits the air brakes to set before
the internal valve opens – even if the truck operator forgets
to set the brakes. The brakes cannot be released until the
internal valve is closed.

In addition, a 4–way actuating valve can be used with
Type C404A32 to pressure both sides of the air cylinder
depending upon the position of the operating handle. This allows
air pressure to close as well as to open the internal valve.