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The part on a slurry tanker that does the most amount of work and is subject to the most wear and tear is undoubtedly the vacuum pump. It works on the principle of removing the air from the tank which creates a vacuum which in turn sucks up the slurry. The pump is also used in reverse to push air back into the tank creating pressure which will spread the liquid once the gate valve is opened.
The vacuum pump normally used is a rotary vane pump which consists of vanes mounted into a rotor that rotates inside of a cavity or chamber. The centres of the two rotor ends are offset, causing eccentricity. The vanes are allowed to slide in and out of the rotor and seal against the edges which creates vane chambers that do the pumping work. Over time especially if not maintained correctly the vanes inside the pump can wear, break or become stuck inside the rotor slots which will drastically reduce the pumps ability to work efficiently and often stop it working altogether.
All vacuum pumps should be fitted with an oiler which drops lubricating oil into the rotor at a rate of at least 1 drop every 2 seconds. This oil lubricates the vanes, only a light grade of oil such as pump oil or hydraulic oil should be used. Take care not to let dirt in when filling by cleaning around the area beforehand. Good practice particularly when working with watery slurry is to suck up a cup full of diesel into the pump when finished which will coat the vanes and stop them sticking. Best practice is to try rotate the pump by hand before attaching the PTO shaft; this will allow you the opportunity to identify a potential problem such as a stuck vane before applying the tractors power to it which may potentially cause more damage. If the pump doesn’t rotate freely you should free it by hand using the PTO shaft at 90 degrees for leverage. If it doesn`t move you will have no choice only open it to fix the problem. Another sign that there is an internal issue with the pump is that the sound may be different from the normal note, the suction performance may be reduced or worst case scenario it won`t work at all.
In this article I am going to take a step by step look at how to replace the vanes and rebuild your pump which is a relatively simple job which many farmers can do themselves.
The vacuum pump is attached to the draw=bar of the tanker normally with 4-6 bolts. The best practice is to wash the pump with a high pressure washer before working on it as it will make the job much easier not to mention cleaner. In some cases you can rotate the pump to gain access to the rear of it to remove the rotor however the best practice is to remove it completely and put it onto a bench at waist height to work on. Take care when removing the pump as it is quite heavy and should only be lifted with a suitable machine such as a forklift.
The oiler is a critical part of the pump to ensure it stays working efficiently. When the pump is on the bench it is often a good opportunity to clean the oil system making sure it is working correctly. Remove the bolts holding the oil pump to the vacuum pump and remove it taking care not to lose the small drive piece.
Clean and inspect for wear or damage. Replace if necessary.
Replacement oiler kits are available starting at €70 + Vat. These kits will consist of a new oil pump, oilers, pipes and all the necessary gaskets to refit.
When refitting the oil pump take extra care that the drive is in place and aligned correctly. Failure to do so may bend or break the drive attachment and stop the oiler working. This is a common mistake that people make so extra care should be taken when refitting.
The next step is to get into the chamber where the vanes and rotor are. Remove the ring of bolts around the faceplate and refit two longer bolts into the dedicated holes and retighten taking care to have the correct thread.
These bolts are threaded into the faceplate and will remove it exposing the rotor and vanes. Don`t worry about the gasket seal as this will have to be replaced when refitting. You can at this stage remove the vanes although the best practice to do the job correctly is to remove the entire rotor.
To remove the rotor the pump will need to be rotated 180 degrees to the input shaft and gearbox end. Drain the oil in the gearbox into an appropriate container and dispose of it correctly. Once drained remove the studs and again use longer bolts to remove the gear casing.
Once open check the gear and bearing condition. The gears should not have any worn edges or chips missing, if so they will need to be replaced. Check the bearing by rotating them checking for roughness and excessive movement, if ether are present the bearing will need to be replaced.
To gain access to the rotor you will have to remove the two bolts hidden within the gearbox itself. Once removed the gear plate should come off, take care not to damage the oil seal which runs on the shaft.
Check the seal closely for damage or any wear and replace if necessary, my advice is to replace it regardless of condition as oil seals are not expensive, for the sake of it while you have access to it you should replace it.
It is now time to remove the rotor from the chamber. Take care when handling it as it is heavy and will require another pair of hands. Once out the vanes can be removed and the rotor and chamber thoroughly cleaned with a pressure washer.
When clean inspect the chamber for any signs of roughness, if present use a fine grade of sand paper to remove the roughness.
The same principle applies to the slots which the vanes fit into, clean these out and lightly sand to make sure the vanes can slide in and out freely.
Once the slots are cleaned and sanded the next step is to fit the new vanes. When fitting them firstly lightly coat them with pump oil before assembling making sure that they are free to slide in and out of the slots. Vanes that stick or are tight will cause the pump to not run correctly causing problems or damage so it’s vital that this step is adhered to correctly.
Over time the vanes will inevitably wear due to the friction between them and the chamber wall which creates the seal and allows the pump to work. New vanes are relatively inexpensive with prices on average starting at €10 + Vat each.
Once the vanes are fitted it’s simply a matter of reversing the process to reassemble it. Make sure that all surfaces are clean and dry replacing all gaskets and seals necessary. Refill the gearbox with good quality oil such as SAE 90 gear oil. Refill the pump oiler with clean good quality pump oil or alternatively any light oil such as hydraulic oil. Once assembled turn the pump by hand a number of full rotations to ensure everything is working correctly before running the tractors power through it.
While you are working on the pump it is also a good opportunity to check it over in relation to other components such as the pressure relief valve which is a vital safety feature.
Rebuild Kits
To make life easier you can purchase complete rebuild kits to suit the make and model of the pump fitted to your tanker. These kits range in price from €120 + Vat upwards and contain everything you need to do it yourself.
The most important thing when ordering the kit to suit your pump is to obtain the correct make and model of it as well as the serial number which should be stamped into the casing. This will ensure that you get the exact and correct parts needed to do the complete rebuild.
Once completed it is just a matter of refitting it to the tankers drawbar and attaching the PTO shaft.
Dos
· Wash the pump before removal
· Remove if possible onto a workbench
· Take care when dissembling as to where parts go back
· Make sure the oiler is clean and working correctly
· Replace worn or faulty parts
· Use long bolts to remove the faceplate and gear plate
· Take care when lifting out the heavy rotor
· Thoroughly wash the rotor and chamber
· Clean out the vane slots and lightly sand
· Lightly sand any rough spots in the chamber
· Make sure the new vanes are free to move in and out of the rotor slots
· Lightly oil when fitting the new vanes
· Clean all surfaces and replace all necessary gaskets and seals
· Use correct quality oil in the gearbox and oiler system
Don`ts
· Attempt doing anything if you are not mechanically confident
· Reassemble with worn, old or faulty parts
· Force vanes into slots or reassemble with vanes that are tight or sticking
· Not replace gaskets or seals
· Use lesser grade or wrong oils
A small amount of time, some basic mechanical know how and standard tools commonly found in any farm workshop will allow you to refurbish your pump yourself at home in order to obtain many more years reliable service while helping to save you money.
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