This document provides instructions for installing a J.P. Instruments model 201B fuel flow transducer in an aircraft. It describes how to properly orient and position the transducer horizontally in the fuel line with no bends closer than 6 inches, and to ensure correct attachment of inlet and outlet lines. The transducer should be installed between the engine fuel pump and servo regulator for fuel injected engines. The wires connect to the EDM for power and should be routed away from ignition wires.

1. This question comes up often enough so we decided to
write on how best to install the fuel flow transducer
model 201B manufactured by J.P. Instruments in an
aircraft.
Orientation of the 201B fuel flow transducer:
To start off and assuming you have removed the
existing fuel flow transducer, hold up the new 201B
fuel flow transducer in a horizontal position with the
three wires up – because this is exactly how it is to be
fitted. Fitting the fuel flow transducer any other way
will lead to its failure. When the fuel flow transducer
is in the horizontal position, the rotor within it are
proper oriented and aligned with fuel flow. This is
how it is meant to operate. Also, while fitting it, be sure that there is no bend closer than 6
inches either in the inlet or outlet pipe i.e. no bends before or after the transducer. Also, do not
use aluminium or brass fittings when installing the 201B fuel flow transducer – use only
AN816-7 Steel. The transducer is engineered to seal tight so do not use Teflon tape, or other
thread sealant compound of any kind. Also, the transducer is marked IN and OUT for the fuel
lines – so make sure you attach it correctly or the rotor will malfunction. The maximum torque
should not exceed 15 ft lb (180 lbs.) or roughly, two full turns past hand tight.

2. Installation location:
If your aircraft has a carburettor, the fuel flow transducer should ideally be at the same height
as the carburettor. If it is higher, fit an anti-siphon loop in the line that peaks higher than the
transducer. If your aircraft sports a fuel injected engine, fit the fuel flow transducer between
the engine fuel pump and the servo regulator. If your aircraft has that unique vapor return
line, install the fuel flow transducer between the servo regulator and the flow divider (spider).
We have seen aircraft with Fuel Flow Instruments
mounted between the electric boost pump and the
mechanical pump – this is not recommended. Also,
please do not hard mount the transducer to the engine
as engine vibration can damage the internal rotor or
cause it to malfunction and give misleading results.
When installing the 201B fuel flow transducer, the
wires are to be connected to the EDM. The fuel flow
transducer gets its power supply (12V) directly from
the EDM. Also, the wires should not be route along
with or adjacent to ignition wires, alternator wires,
spark plug leads, or cabin heater ignition wires.
When done, set the K-factor. The Fuel Flow
Transducer 201B will have a K-factor of ~29.
Testing:
It might be worthwhile to also procure a Fuel Flow Tester (just $35.00) for testing instrument
and transducer.
Fault finding:
Some pilots called in to report consistently high fuel flow readings. If you have followed above
installation procedure correctly, check for air entering system at selector valve (may require a
change of the O-ring). Here’s a test: The next time the aircraft is flown in cruise, turn on the
boost pump for one minute. If the fuel flow drops, then this is an indication that air is leaking
into the fuel line upstream of the transducer. It is possible that air is leaking into the system
through the seal valve or other connection. Fuel stain may not be visible.

3. JPI Sales:
1-800-345-4574
714-557-3805
FAX: 714-557-9840
sales@jpinstruments.com
JPI Technical Support:
1-800-345-4574
714-557-3805
support@jpinstruments.com
J.P. Instruments Inc.
3185-B Airway Ave
Costa Mesa, CA 9262