Pump Doctor

Slurry pumping in its simplest form can be divided into three catagories; light, medium, and heavy slurry. Below please find a rough definition of what constitutes each slurry.

Light Slurry:

• Presence of solids is primarily unintentional
• Solids size typically < 200 microns
• Non-settling slurry
• The slurry specific gravity < 1.05
• Less than 5% solids by weight

Medium Slurry:

• Solids size 200 microns up to 5mm
• Settling or non-settling slurry
• The slurry specific gravity < 1.15
• 5% to 20% solids by weight

Heavy Slurry:

• Slurry's main purpose is to transfer material, i.e. sand & gravel
• Solids > 5mm
• Settling or non-settling slurry
• The slurry specific gravity > 1.15
• Greater than 20% solids by weight

Velocity. Blockages can be attributed to one of two reasons. Firstly have you calculated your product velocity through the pipeline correctly? If you are pumping a slurry with solids if you do not maintain a suitable velocity through your pipeline then the solids in suspension will drop out, eventually leading to the blockage of the pipeline. Secondly is the pipeline large enough for the solids being pumped? Depending on the quantity of solids being pumped you should always leave a good margin to allow for the passage of your solids.

Seawater Applications. Historically submersible drainage pumps have been used in seawater applications. However as the pumps are made of a lightweight material (aluminium) the pumps can have a limited life in this application. The longevity of the units can be extended by fitting the pumps with sacrificial zinc anodes, but these need to be checked and changed on a regular basis. As an alternative Grindex now offer a range of drainage and sludge pumps manufactured in 316SS to counteract the effects of seawater.

All the Grindex Tetra pumps are fitted with an air valve, as were all the the previous series of Grindex drainage and sludge pumps. The purpose of the air valve is to prevent the pump from burning out should the pump be starved of water. The air valve is a simple mechanical device that relies on water pressure to stay closed. When the water pressure drops, because the sump is empty for example, then the spring at the back of the air valve opens. This allows the pump impeller to operate much like the fan on a standard IP55 motor blowing air around the motor and out the air valve. The pumps can run for many hours in this situation without incurring any damage. Then when water begins to flow into the sump again the pressure of the water being pumped around the casing closes the airvalve and the pump begins to operate normally. We used to demonstrate the effectiveness of the air valve at trade shows by leaving a 240V Minex running on the stand all day under lights. We never got one to trip in all the years we did it. So yes, the air valve really does work.

There is always a manufacturers recommended service interval. With Grindex pumps the inspection interval is recommended at 2000 hours of operation, where as with Toyo pumps the recommended interval is only 500 hours. Why the difference? The simple answer is that your service interval should relate to the hours a pump is doing in its normal operating state. Therefore a Grindex pump, for example a Major 'N', operating in an environment where the water is clean and non-corrosive should run for at least 2000 hours without generating any issues for the owner. A Toyo pump working in its normal environment, for example mill scale, which is highly abrasive as well as potential corrosive, needs a much more frequent inspection.

Service intervals for pumps are no different from service intervals for cars, if you do not follow the manufacturers recommendation then you run the risk of seriously damaging your pump. To extend the analogy a little further you do not have to have the pump serviced by the manufacturer or dealer, it can be done by your local repair shop or pump distributor. Just make sure that they are familiar with submersible pumps. If in doubt ring us for advice (it's free!). 

Grindex submersible pumps can be used in series. Although not exclusive throughout the range a certain number of the drainage pumps can be fitted with what is called the tandem base. This replaces the bottom plate on the pump and allows for a suction pipe to be fitted directly on the pump at the lower diffuser. The advantage of this is that the pumps can be used in booster applications, much as you would use a standard centrifugal surface pump, with the advantage that it is still IP68. This is particularly useful in any underground situation, such as a tunnel or mine where long distance pumping is involved and the danger of flooding is high. It is also very easy to convert the pumps back to their standard configuration should you wish to use them as stand alone submersible pumps at a later date.