Inspection and Testing Gas Piping:
The building structure should not be weakened by
in stall ing the gas pip ing. The piping should not be
sup port ed by other piping, but should be ﬁ rmly sup-
port ed with gas hooks, straps, bands or hangers. Butt
or lap welded pipe should not be run through or in an
air duct or clothes chute.
Before turn ing gas un der pres sure into pip ing, all open-
ings from which gas can es cape should be closed.
Im me di ate ly after turn ing on gas, the system should
be checked for leaks. This can be done by watching the
1/2 cubic foot test dial for 5 min utes for any movement
or by soap ing each pipe con nec tion and watch ing for
bub bles. If a leak is found, make the nec es sary re pairs
and re peat the above test.
De fec tive pipes or ﬁ ttings should be replaced and not
re paired. Never use a ﬂ ame or ﬁ re in any form to lo cate
gas leaks — use a soap solution.
After the piping and meter have been checked com-
plete ly, purge the system of air. DO NOT bleed the air
inside an enclosed room.
During pressure testing of the sys tem at test pres sures
in excess of 1/2 PSIG, the pressure washer and its
individual shut-off valve must be dis con nect ed from
gas sup ply pip ing system or damage to the gas valve
will oc cur.
The incoming gas pressure must be a minimum of
9.0 wc-in and must not exceed 13.8 wc-in or ½ psig
to the control valve. Line pressure above ½ psig must
be regulated prior to the machine. The ideal supply
pressure is 13.0-13.5 wc-in. If the required BTU input
can not be achieved consult the factory for instructions
regarding changes to the nozzle oriﬁ ce size and an
appropriate manifold setting.
NOTE: Any changes to the burner and manifold pres-
sure setting should only be performed by a trained
technician and adjusted using a ﬂ ue gas analyzer.
The manifold pressure has been preset at the factory
according to the table below for optimum operation at
sea-level. The manifold pressure and BTU input will
be listed on the speciﬁ cation plate for the machine.
For Tech Tip Instructions
Combustion efficiency in a natural draft pressure
washer is signiﬁ cantly inﬂ uenced by the heat created
inside the coil, the design of the coil and ﬂ ue and the
length and diameter of the exhaust stack. The table
below shows data included in the operator's manual
for ﬂ ue and stack sizes and gas manifold pressure
settings. These sizes are critical for achieving proper
combustion and acceptable emissions.
Testing has shown that simply adding a 36" stack
extension to the ﬂ ue adapter on top of the pressure
washer can reduce the outlet temperature by 5-10°F.
This occurs by inducing a higher pressure differential
at the exit of the coil and increasing the ﬂ ow of air into
the combustion process and through the stack. Most
or all of the lost outlet temperature can be recovered
by installing and adjusting a damper in the stack.
However this adjustment must only be performed by
a trained technician using a combustion analyzer. An
adequate combustion analyzer can be purchased for
a little at $500 (Bacharach Fyrite Tech, Testo 310).
The analyzer must determine percent oxygen and/or
percent excess air as a minimum.
The damper should be installed 24-36" above the ﬂ ue
adapter. The pressure washer can be operated safely
with the damper fully open but with the lower outlet
temperature. If the damper is closed too far there will
not be enough oxygen to burn all of the fuel. This will
cause higher and potentially dangerous levels of CO
in the ﬂ ue gas emissions.
To adjust the damper for proper combustion and ef-
ﬁ ciency perform the following:
1. If there is no sample port for the analyzer probe,
drill a hole slightly larger than the combustion analyzer
probe through the exhaust stack at a point about 18"
above the ﬂ ue adapter.
2. Insert the probe of the combustion analyzer so
that the tip is at the center of the stack.
3. Open the damper to the fully open position.
4. Start the pressure washer and allow it to heat up
for at least 20 minutes before making any adjustments.
5. Note the values for % Excess Air and/or % Oxygen.
6. Close the damper in small increments until %
Excess Air is between 20-30% and/or % Oxygen is
9.801-509.0 - C • Karcher Operator's Manual