The NZET SWAB User Guide
Objective:
To effectively clean all loose deposits, slimes, and other residues from the internal water supply
mains that form part of the authority's water distribution system. The user guide covers the use
of polyurethane foam swabs for the periodic cleaning supply mains and service lines.
The use of polyurethane foam swabs for removal of loose deposits in water supply mains is a
well accepted procedure. Comparative trials have demonstrated a superior performance in most
situations when this method is compared with the alternatives, water flushing or air scouring.
Materials:
Different grades of swab are available and suitable for different applications. Note the term
"swab" applies to light flexible polyurethane foam cylinders, with tapered noses. The heavier,
less flexible bullet shaped devices, often incorporating hard abrasive coatings are correctly
known as "pigs".
Experience and comparative trials have shown that whilst there are economies in the cost of the
swabs to be made in using low density highly flexible polyurethane, a better cleaning result is
usually obtained with a reasonably hard foam. A good compromise between flexibility and
hardness is the grade "'SH" or "severe hard' foam. This has specifications of; density 27 - 29
kg/m3,. Hardness 23 - 27 kg, and static fatigue 6%. (Definitions and measurements are in
accordance with BS3379).
This gives a foam which retains its shape better than lower grades and therefore, for an
equivalent size, exerts a greater pressure on the pipe wall. Flexibility is kept to a which ensures
that launching and exiting into and from the reticulation system a achievable using standard
techniques.
The use of a solid base on the swab increases further the degree of compression and motive
force obtained in a given application. This improves cleaning, and bonds swab together in
situations where rapid disintegration may otherwise occur. It does however have the
disadvantage of making the swab less flexible, and therefore prone to blocking under conditions
such as hydrant launching. As the bases are applied manually to the cut swabs, there is also a
significant additional cost associated with the solid base.
Sizing:
The desirable size for a particular application is a function of a number of factors, particularly;
pipe internal diameter condition of pipe interior nature of material to be removed launching and
recovering methods
As a general rule, the swab diameter should be in the range 10 - 40% greater than the pipe
diameter. Swabs should also have a length to diameter ratio of at least 1.5 prevent tumbling
and assure a reasonabty1ong surface for wall contact. A taper nose of the swab will assist its
launch and passage through obstructions.
Launching and Exiting:
If there is an opportunity for the swab to move in the wrong direction on launching through a
hydrant with a line valve located other than next to the hydrant, then it should be full of water at
the time of launching.
The use of lubricants such as medlube or dish washing detergent and presoaking the swab in
clean water are recommended for all launch situations.
Sending multiple swabs launched simultaneously is not recommended, although launching at
approximately 5 - 15 minute intervals for long lines appears to be satisfactory .
Hydrant launching may be undertaken by inserting the swab up a hydrant stand pipe or
specialised swab launcher. Flow is fed through this from a fire hose connected to a remote
hydrant, or, if this is not possible, from a water truck with a pumped outlet. Required launching
pressure varies, however, generally 30 - 40m head of water more than adequate, as pressure
reduces from this, some hydrant launching becomes marginal. Hydrant launching can also be
undertaken by removing the top of a screw down hydrant and inserting the swab into the main
with a clean broom handle.
At least one NZ authority undertakes the maintenance of hydrants and hydrant upstands in
advance of swabbing operations. This has the advantage of ensuring smooth launching and
recovery whist also undertaking necessary cleaning and I which ensure that the hydrants are
able to deliver full flow under fire conditions, have leaks and other faults identified and repaired
more rapidly than would other wise
occur.
The swab, unless blocked somewhere, will always follow the flow of water, hence the need to
isolate the section of line and control the inlet and outlet points.
Launching and exiting through hydrants should always occur with the hydrants fully open to
minimise the potential for blocking within the hydrant.
Swabbing Operation:
In most situations, prior to swabbing, consumers should be notified, and consumer connections
turned off for the period of the cleaning operation plus subsequent flushing and bleeding of air.
The recommended swabbing velocity is in the order of 0.8 m/s. This equates to a moderate
walking speed. If the velocity is too high, areas will be missed, if too low, insufficient scrubbing
action will result.
Control of the swab velocity should be undertaken at the upstream end, by varying the rate of
flow of motive water. Generally 1 - 3 turns open of a conventional waterworks sluice valve will
provide sufficient flow and pressure.
Location of the swab can be determined by either observing the highly discoloured water
passing successive turnout points on long lines, or, for greater accuracy, the attachment of a
locating device which emits a signal and the use of a specialised receiving transmitter.
Usually failure of the swab to appear will be due to a failure to launch, (no dirty water appears at
outlet)or, a failure to exit, (outlet runs dirty then clear again). Blockages within the line are rare
and can usually be rectified by backflushing the swab out the inlet point. Butterfly valves, even
in fully open position, have been known to stop passage. Pressure reducing valves and any
other fittings providing significantly
than full bore flow should also be avoided.
If a true blockage does occur, water will bypass the swab so delivery will still be possible, albeit
at reduced pressure. Location can be undertaken by rodding on smaller lines, or, sending down
a second swab with a locating device on more lines. Removal is then a matter of digging up and
breaking the line, however, in cases where this has happened, the object causing the blockage
is something that was better removed. An example found in one NZ town was a length of 50mm
x 75mm timber in a 100mm diameter fire main!!!
A significant enlargement in the pipe diameter may also cause a situation where swab ceases to
move. This occurred in a submarine line in one NZ situation, where the pipe had been
previously fouled by a fishing vessel and repaired in a significantly larger diameter.
Unfortunately the larger diameter had not been noted on the plans.
Care should be taken with the disposal of swabbing water. This should ideally be analysed if
the nature of contaminants is unknown, ie when doing the first swab in a town, and the disposal
based on the nature and level of contaminants and .................... most urban situation,
discharge to stormwater via a hydrant standpipe free flowing onto the road surface should not
present any problems.
The above points also highlight the importance of good planning and research prior to the initial
swabbing of any section of main. Swabbing exercises should start at the source or treatment
plant/reservoir and be conducted in the direction of system.
Disclaimer:
This user guide is provided with the NZET Vitaswab product as a service to product users. it is
based on the best available experience on this product both in NZ and overseas. No liability,
however, either direct or consequential, will be accepted by NZET for for problems arising from
the use of the Vitaswab product in compliance with this guideWe are currently creating content
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