WATER JET CONFERENCE - Waterjet Technology Association

equired, and although it is convenient in other water jetting situations, in a fixed
installation this is not always found to be desirable.
5. The speed of the pump could be increased or decreased with a variable speed motor,
thus increasing or decreasing the volume of water. Eventually, the last solution was
used, but as only two pressures were required, then a double wound stator was used
and it was found that without changing the nozzles, simply by changing a connection
on the motor winding, that the motor would rotate at either 1450 rev/min or 960
rev/min. The pressure being approximately inversely proportional to the flow,
therefore, the higher speed rotation of the pump gave 10,005 PSI and lower rotational
speed of the pump gave a pressure of 6,525 PSI. This simplified the operation of the
speed changes or pressure changes for the operator. He could merely move a lever on
the starter which was indicated 'high pressure' or 'low pressure'.
So, as a door was removed, it was examined and the pump started at the required
speed. Eventually, after the ovens had been used for about 3 times and all doors were
kept clean by the lower pressure of 6,525 PSI, this saved pump power, use of water,
pump wear, gland wear, nozzle wear and was generally thought to be the most efficient
way of using the jet cleaning system.
DESIGN SOLUTIONS
The first cleaning machines were to be used on the coke side which generally has
a more difficult problem with door sealing, as the hot coke is passed through this side of
the oven. The coke guide machine is fairly small as it merely has the door extracting
facility; a separate trolley car is towed behind the door extractor, which is quite a simple
openwork structure. There was difficulty to find space to accommodate quite a large
pump, 125 hp unit and a 400 gallon tank. The size of the tank was determined by the
number of cleaning operations or pushing cycles required per shift and in order not to
interrupt the flow of coke pushing, it was planned that the tank would be filled at the
beginning of each shift. The tank was placed as high as possible in the coke guide
machine to give a positive head to the triplex plunger pump, low level alarm and
shutdown facility ensured that low level of the tank would either stop or inhibit the
starting of the pump, this protected the pump from dry running.
High pressure water is fed through a pulsation damper and a high pressure hose to
the nozzle cleaning lance. Special attention had to be paid to the gland of the pump to
ensure that the coal dust and ash dust which penetrates every corner of the door
extracting machines did not affect the plunger seals and crankcase oil seals (see figure 6.)
The tracing motion which originally carried the scrapers had to be redesigned to
take the water jetting lance. The first design of the tracing motion carried two cleaning
lances each on cleaning one half of the track around the periphery of the door seal.
Eventually, this was replaced by one single lance, which rotated completely around the
periphery of the door seal.
OPERATING EXPERIENCES & CHANGES TO DATE
Early use of the door cleaner in production had some problems with the lance
becoming bent due to the buildup of tar on the door plug. This led to refinements on the
hydraulic drive of the tracing motion. A relief valve was fitted so that if an obstruction
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