Fisher N551 - Operation; Installation; Specifications

Types N551 and N851
2
Specifications
The Specifications table lists specifications for the Types N551 and N851 valve which is designed for butane, propane
or NH
3
service at ambient temperatures. Contact your local Sales Office if the valve is to be used on any other service,
fluid, compressed gas or temperature condition.
Maximum Inlet Pressure: 400 psig / 27.6 bar
(2)
Operation
CAUTION
The Type N551 handle and shaft may break if
the valve is forced open against the gas ow
and before pressure is equalized on each
side of the main valve disc.
To Open a Closed Valve:
Close a shutoff valve downstream of the Type N551. Pull
the Type N551 handle counterclockwise. There will be an
opening as inlet pressure helps hold the valve disc closed
against the seat. The initial opening force on the handle
opens a pilot valve in the main valve disc, permitting
pressure to build-up downstream. When differential pressure
across the main disc has been reduced, the Type N551 can
be opened without further difficulty by continuing to lift the
handle to the open position. When the handle is fully open
(handle perpendicular to the pipe) the latch engages to hold
the valve open.
CAUTION
Because the valve is spring closed (aided by
pressure), the handle can snap down with
considerable force when closing. Keep hands
and ngers away from the handle as it closes.
To Close an Open Valve:
Pushing the handle down (handle parallel to the pipe) will
close the valve.
From a remote location, pulling on the remote cable or
exhausting pneumatic pressure from the Type P327D will retract
the plunger allowing the Type N551 to close. If emergency
conditions cause the fusible element to reach a temperature
of 212°F / 100°C, the element, which attaches the handle to
the shaft, pulls apart and allows the valve to close.
Installation
Shutoff Direction
The valves shall be installed in the fixed piping between a
storage tank and the transfer hose connection at the truck or
tank car loading/unloading area. They can be placed in a line
used either for filling or withdrawing from the storage tank
(or both). The valve shall be installed to shutoff flow from the
tank towards the hose, enabling the valve to control product
loss in case of a hose break.
!
WARNING
The Type N551 valve is a spring closed (aided
by pressure) and shutoff ow in one direction
only. THE NAMEPLATE FLOW ARROW SHOWS
FLOW DIRECTION FOR VALVE SHUTOFF (see
Figure 6). The arrow shall point to the hose
connection. Improper ow direction will not
shutoff ow through the line.
When installed in horizontal piping, install with the nameplate
up. The valve can be installed in vertical piping with the flow
arrow pointing to the desired flow direction for valve shutoff.
In some cases the normal flow through the valve may be
opposite the shutoff direction (like a back check valve).
Bulkhead Protection
The valve should be installed near the hose connection, but
shall be positioned so that any undue strain resulting from a
hose pull cannot shear the valve or its inlet piping from the
storage area piping. The piping shall always be firmly supported
and anchored to be sure of meeting the requirement.
One preferred method of installation is shown in Figure 2
where the pipe connection to the valve and to the hose
coupling is securely anchored in a solid bulkhead.
A bobtail truck can provide enough pull on the hose
connection to cause a break in the system. That break must
not occur between the Type N551 and the storage tank.
TYPE BODY SIZES, NPS*
PROPANE FLOW AT 2 psi / 0.14 bar
DIFFERENTIAL, GPM / l/min
N551-10, N851-10, N851K-10
(1)
1-1/4 FNPT 150 / 568
N551-16, N851-16, N851K-16
(1)
2 FNPT 295 / 1117
N551-24, N851-24, N851K-24
(1)
3 FNPT 850 / 3127
Temperature Capabilities: -20 to 160°F / -29 to 71°C
1. FFKM (Kalrez
®
) gasket and seals.
2. The pressure limits in this Instruction Manual and any applicable standard or code limitation should not be exceeded.
* Nominal Pipe Size.
Kalrez
®
is a mark owned by E.I. Du Pont de Nemours and Co..