- Equipment
Recommended air compressor to be a minimum of 375 cubic feet per
minute (cfIn) and a maximum of 850
cfm. Some people confuse pressure with volume. If we think of
a small portable tank that is pressurized to
100 psi., it would be fme to fill a bicycle tire with. However,
if we connect the same tank to our large irrigation system it will accomplish
nothing. To utilize a properly sized compressor, a 2" outlet complete with a 2"
supply hose is essential. These 2" bull hoses are actually equipped with 2 3/4"
end fitting_. Hence, it is important to ask for an adaptor from this 2 3/4" size
to a 2" standard pipe thread (npt).
Connect the compressor to the pump station manifold. If you
obtain an 850 cfm machine, it is advantageous for you to use two separate 2"
supply hoses. This will help to accommodate the extra volume of air the 825
machine can supply.
Other useful equipment can be an as-built irrigation drawing,
manual flag key for valve-in-head sprinklers and a watch. Most of the irrigation
systems are automatically controlled these days, and if you are among this
group, the blowout procedure is a one person operation.
More than one will only cause delays and confusion to what is
and what has not been blown out. In addition, it is very common for a
multi-person crew to fire up too many outlets, and thus drastically drop the air
pressure to a point where nothing is being accomplished.
b. Starting
Shut down the power to all pumps. Leave all field isolation
valves in their open position. Blowing out certain sections at a time does not
work out very well in most cases. To maximize efficiency, it is important the
operator understand some basic principles of water, air and piping systems. As
we discussed in the Spring Start-Up article, air compresses and water does not.
The piping system is basically full of water and it takes very little air volume
from the compressor at the beginning of the blowout process to bring the system
right up to perhaps 100 psi. This allows us to operate a large number of
sprinklers initially for a relatively short period of time. During this time
frame however, it will be possible to purge a large percentage of the water in
the system.
This is one of the key maneuvers in producing the most efficient
and expedient blowout. During this first hour or two, depending on the size of
the system, we want to see solid water being dispersed by the sprinklers.
Sprinklers with long runs and are dead ended, are ideal candidates for being
turned on manually via the flag key. These units will run an extra long time
discharging solid water strictly because of their positioning in the system.
Pond fill outlets may be used initially, but all outlets including sprinklers
emitting serious amounts of air should be turned off. This will contribute to
maximizing the water removal from the system by retaining air pressure.
c. Cycling
With air becoming prevalent throughout the irrigation system, it
becomes time to start syringing satellites. All satellites will eventually be
syringed multiple times each at two or three minutes per station. Now that the
piping system has become higher in air content versus water, the pressure gauge
at the pump station should indicate a decreasing value. You will find the
blowout works well at about 40 psi, with 30 being marginal and 50 being high.
Air flies through the piping system at speeds of more than 50 times that of
water. This is part of the reason 50 lbs of air is very significant, where as 50
lbs of water is not. The pressure gauge on the compressor will likely read about
70 psi, but this is not the real pressure inside our piping system, only a
reflection of the backpressure and friction caused by the 2" bull hose. If the
system has been mostly flushed of water and the air pressure exceeds 50 psi on
the pumping station gauge, you will likely destroy the sprinkler internal
assembly as it pops up. Normally, water cushions the sprinklers when they first
pop-up and seat. With air only and because of the speed of the air, the
sprinklers can snap onto their retaining seat hard and fracture. Hence, if this
high pressure situation arises for one reason or the other (you fell asleep or
took an extended fall lunch break {Teaser's}), close the ball valve on the
compressor and open the drain tap at the pump station to relieve the pressure.
Once it is below fifty, start multiple heads on a distant satellite. Then begin
syringing other satellites, reengage the compressor and shut down the first
satellite with the multiple zones.
Once air becomes visible on most of the golf course, retime the
satellite syringe memory to one minute. Start three or four satellites on a
complete syringe mode. Once these units start to syringe their larger fairway
stations, check the pump station to ensure there is still adequate pressure. If
not, shut down all of them, wait five minutes and start two of them up, perhaps
starting on the first fairway station of each unit. It is a process that is
repeated over and over until small amounts of thin white vapor are all that
appear from each sprinkler. It is imperative the operator see every single zone
of each satellite when in the finishing stages to satisfactorily complete the
job.
d. Finishing Touches
Blowout the pressure relief valve at the end of the
procedure, decrease psi setting on the valve to do so, usually three full turns,
and then reset.
When you are completed, do not let the remaining compressed air
from the irrigation system escape at high velocity from the compressor
connection point. It is best to let the system decompress on it's own over
several days. This is why it is imperative to have a shut off valve at your
connection point. Picture your irrigation system as a huge balloon. If you open
the end, all of the compressed air in the system is trying to escape out the
same large outlet, bringing with it every drop of water remaining from the
entire piping network. Some of it will escape at the pump station, much of it
will fill your mainline as the pressure quickly decreases. When this happens,
you've got problems. This relatively small amount of water would not have been a
problem spread throughout the piping system, however, pooled all together in one
spot can cause a lot of grief.
Open all drain plugs on the pumps (bottom to drain and top to
vent)
Leave all ball and butterfly valves in the open position
throughout the station. This will allow any trapped water to freeze and expand
without breaking anything. Only when we lock it into an enclosed space with no
room for expansion is when damage is incurred.
If you have an insulated pump house and are going to run a small
heater, those of you with centrifugal pumps and a wet well, need only to drain
the upper portion of the suction lines. This will automatically be done when you
remove the drain nuts from the pump case.
Wet well owners can also drop a cattle trough type water heater
into the wet well. It is economical to run, and it will prevent an ice build up
in the well even if the pump house is not heated.
Turn power off to satellites when finished, leaving them on
won't hurt the units directly, but the heat from the transformers within the
units acts like a flashing neon light billboard for mice thinking they just
found "Park Boulevard" in Tuxedo.
Open all pond fill valves a fraction (10% maximum) after the
blowout is complete. This will allow any small amounts of water to drain out,
but not large enough to let any rodents into the system.