Revision 1
I.
Use of Lances and Nozzles
1.
Lances - Lances which are rigid or semi-rigid having nozzles fitted
to
with any
combination
of
forward, backward or 90 degree angle jets shall be used with either a
dump system or dry shut off control valve. When a flexible lance
or nozzle mounted
on a hose is in use, the jet should not be operated at pressure unless the nozzle is
properly positioned inside the work piece, or the lance operator is protected by screens
or proper shielding from rear facing jets.
If
necessary, the lead-in
to
the work piece
should be cleaned by other methods.
2.
Flexible lances - Flexible lances used
to
clean pipes, where the inside diameter of the
pipe is not small enough
to
prevent the lance from turning back on itself, shall have a
piece
of
rigid straight tube, slightly longer than the diameter
of
the pipe, fitted
immediately behind the nozzle
to
prevent this from happening.
3.
Distance indicator - When an assembly is used which allows the nozzle to enter the
work piece with restricted visibility, the lance, hose or floor should be clearly marked
in a manner which enables the lance operator to judge how far the nozzle is in the work
piece before pressure is applied and, conversely, so that pressure is released before the
apparatus is completely withdrawn from the work piece.
4.
Lance length - The length of a rigid lance or combination
of
lances shall be such that
the lance operator can maintain control at all times.
5.
Jet
pressure - The nozzle and minimum operating pressure shall be selected by the
lance operators
to
allow effective and efficient high pressure water jetting.
6.
Improper
use - Should a lance operator enter a manhole or access port for any
purpose (preferably with the high pressure water jetting unit turned off), the hose shall
not be used to support his weight when climbing up or down.
7.
"T"
pieces - When using a "T" piece or nozzle carrier
"T"
(devices for producing two
(2) equal and opposite water jets at the end
of
the lance and at right angles
to
the
normal flow), it should be inserted into a tube, a vessel, or between two (2) surfaces
before the system is pressurized. This is necessary
to
ensure that should one (1) water
jet be larger than the other, or one (1) water jet become blocked or partially blocked,
the operator
of
the lance will not be spun out
of
control. When a
"T"
piece is used
to
provide a balancing jet on a long lance
to
clean a single surface, it is not always
possible
to
check for equal thrust from both jets in the manner described above,
therefore these lances should be checked by progressive pressure increases. This
restraint shall also apply
to
any form
of
multi-jet nozzle, the jets issuing from which
having a radial component.
8.
Confined working - Before entry into a confined work space for high pressure water
jetting, a certificate
of
clearance shall be obtained
to
ensure that access is safe.
© Copyright January,
2001
NLB Corporation
2-26
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