| Every pump operator
needs to know how to draft, but few do so confidently.
Drafting failures are usually the result of operator
error, because of a lack of proficiency, but confidence
is easily attained with training. With a little
practice, an average crew (two to three firefighters)
can set up a three-tube draft in less than three
minutes.
Drafting is not totally reserved for rural areas.
An existing fireground supply from a hydrant can
be augmented by adding another LDH line and engine
drafting from a nearby static source. This allows
the draft pump's potential to be exploited. A
pump will be more efficient from a static source
since there is no hydrant restriction.
Drafting is relatively simple when a few rules
and limitations are considered. Correlating lift,
vacuum, atmospheric pressure, and the area's elevation
can be confusing. These drafting considerations
are important; however, you may be confident that
a reasonably placed pump at a static water source,
located anywhere on this earth, will produce water.
The pump may have limitations related to lift,
but it should produce water.
When a pump doesn't produce water, it usually
isn't the pump; it's the setup. The pump is a
predictable component. The real question is: Will
there be enough atmospheric pressure to overcome
what the pump operator believes is a "reasonable
hard tube setup?"
The pump's dependable lift is the height that
water can be expected to rise upward from a static
water source and provide a continuous reliable
fire flow. Learn the area's dependable lift expectations
through practice. Realistically, the highest lift
an operator would want to overcome is about 10
feet, and the lift limitation becomes greater
as the area's elevation increases. More importantly,
higher lift requirements will reduce the quantity
of water available to the pump; therefore, high
lift attempts are counterproductive. Get the pump
as close to the source as possible, preferably
requiring less than 10 feet of lift.
Don't confuse a 10-foot lift with the tube distance.
The water source could potentially be blocked
by 30 feet of brush, requiring a multiple tube
operation. A multiple-tube operation does create
some additional resistance for the pump; however,
the lift requirement is the critical consideration.
High spots and dips in the tube can trap air and
inhibit operational efficiency. Avoid bottom feeding
and silt suction by using a floating strainer
or rope to hold the barrel strainer off the bottom
of the static water source. Conversely, ensure
that the strainer makes it to the bottom deep
end of a swimming pool.
The primer evacuates air from the pump and hard
tubes as atmospheric pressure forces water towards
the impellers. From primer activation until the
pump creates pressure should take no longer than
30-45 seconds. If the pump is unable to produce
water in this time, the setup should be suspected
and evaluated. If it is an initial engine placement
error related to the lift requirement, the engine
must be repositioned. The hard tube/pump setup
with a vacuum leak is easily isolated and corrected.
The problem will be in the hard tube connections,
open drains/discharge, or even the tank-to-pump
valve.
Centrifugal pumps like back pressure. Avoid back
pressure fluctuations by operating valves slowly
and smoothly. Back pressure fluctuations are arguably
the most common reason for loss of draft. Opening
a discharge valve too quickly will allow air from
the supply hose into the pump, pushing the water
away from the pump and back down the tube. The
key to successful drafting is opening the discharge
valve slowly until a solid water flow/back pressure
has been established in the line being supplied.
Attempting to rush this aspect of the operation
will ultimately lead to loss of prime.
An engine can be equipped with a second separate
primer unit specifically for the front suction.
This option gives the pump operator the ability
to accomplish the initial draft and water flow.
When time permits, the front intake can be placed
in service with another set of tubes to increase
flow without disturbing the initial water distribution.
Providing the pump with another pathway to introduce
water will reduce the operation's restriction
and increase flow potential. Drafting with an
engine using two large intakes will produce more
water than the pump manufacturer's rating. This
resistance reduction can also be applied to portable
pumps using an intake adaptor and larger tube;
this enhances the portable pump's flow.
If the pump cavitates at the static source, the
pump operator is simply demanding more water than
the pump can deliver with that particular setup.
The pump and hard tube setup has restrictions
such as pump intake piping, tube size/length,
and lift. Cavitation is simply an imbalance between
supply and demand and is one of the best indicators
of the drafting operation's limit. Briefly taking
the pump somewhere near cavitation will determine
the operation's capability. A supply pump's prolonged
cavitation situation will have a global fireground
impact.
Required equipment on a drafting vehicle should
include 2,500 to 3,500 feet of LDH, a variety
of water pick-up appliances, and the necessary
adaptors needed to work with surrounding engines
and hose. A draft engine should carry four to
five tubes. A three-tube operation is about the
most restriction a pump will want to encounter
from a single large intake. However, the extra
tubes allow the pump operator to place two large
intakes in service simultaneously to enhance the
pump's flow rate ability. The extra tubes can
also be used for open relays, portable pumps,
or for another engine's operation.
Ladders, tarps, and pike poles are used for water
retention. Retaining the flow of even a small
stream and using a low-level strainer can produce
a surprisingly acceptable supply rate. An LDH
drafting-specific vehicle will also have a chainsaw
for cutting ice or small trees inhibiting access
and a portable pump capable of respectable short
distance LDH flows. The portable pump flow can
supply a Class A Pump from a remote static source.
An engine with a large hosebed can easily house
3,000 feet of five-inch hose. That's what makes
drafting vehicles unique; they're built with a
specific purpose. The draft-specific vehicle will
have a large hosebed, a short wheelbase, and piping
that reduces resistance.
Creating a water preplan book with distances
from static sources is critical. This invaluable
information will determine the draft operation's
potential before the engine leaves the station.
Drafting practice and observation of a few guidelines
will assist the firefighters in becoming confident
in their drafting operation skills. Don't pull
higher than 10 feet of lift and don't use more
than three tubes together. These considerations
dictate the initial engine placement. When water
is pulled to the pump, open the discharge gate
valve slowly until water flow/back pressure has
been established and pump pressure fluctuation
has subsided.
Any firefighter who practices drafting operations
will become more confident in his skills, and
will develop a greater tactical awareness for
supply operations on the fireground. Good officers
come from strong pump operators.
Jeff Welle is a career paramedic, firefighter,
and registered nurse. For more information on
drafting, LDH relays, and easy fire ground hydraulics,
please visit the Web site: hydraulics4jakes.com
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