How to keep on pumping up the slurry volumes
I was recently asked to repair a slurry tanker which had a recurring problem of passing slurry through the pump when the tanker got full.
The vacuum pump is specifically designed to handle air only, so if slurry makes its way into the pump, it will damage the pump very quickly, leading to an impending overhaul.
The principle of a vacuum tanker is simple. It uses air in either a positive or negative pressure to suck in or blow out the load of slurry.
To fill the tanker, a vacuum is created inside the barrel when the pump is set to remove the air from the barrel. Once the gate valve is opened, this vacuum draws the slurry in through the suction pipe and fills the barrel.
Once you reach the field, the pump is set to pressure mode and blows air back into the barrel to create a positive pressure inside the barrel.
When the rear gate valve is opened, this pressure forces the slurry out through the splash plate or whatever applicator might be fitted on the tanker. For the tanker to remain operating at peak efficiency, the vacuum pump is the heart of the operation and so it must be kept in good operating condition.
Key steps in regular maintenance include:
1. Ensure there is enough lubricating oil in the reservoir of the pump, and that it is of the viscosity recommended by the manufacturer;
2. It is very important to ensure the oil droppers are set to the correct dosing rate. Consult your operator's manual, but a good rule of thumb is one drop of oil per second;
3. Check the level of oil in the gearbox and change it regularly. This gearbox holds a very small quantity of oil so it can overheat quickly.
Even if you undertake regular maintenance of the pump, you may find that its performance wanes over time. A pump operating at peak efficiency should fill a tanker in approximately four minutes - any longer than that and the pump probably requires attention.
If the performance of the pump reduces, there are a number of possible causes, but the most likely is that the vanes of the pump have become worn over time and need replacing.
All slurry tankers have two built-in traps to prevent the barrel from over-filling with slurry, and thereafter making its way down into the pump. However, in this case (right), both of the built-in traps were failing. I therefore had two issues to contend with; I needed to figure out why the traps were failing and allowing slurry past, and remedy that problem.
And secondly, I needed to fully rebuild the vacuum pump and undo the damage done by the slurry having entered the pump.
The photographs and captions opposite provide an eight-step approach to repairing a slurry pump.
The vacuum pump is the key to efficient slurry spreading and any problems can prove costly and time-consuming. In the first of a two-part series, Jamie Casey has an eight-step guide to keeping pumps working at peak capacity
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