Frequently Asked Questions
Q. How can you minimise the headloss through a Grit King® separator?
The design programme will calculate the headloss. We recommend that the inlet velocity is between 1.0 m/s and 1.5 m/s at peak design flow and it may be necessary to adjust the inlet pipe diameter to maintain this. The system headloss will vary accordingly and it will be in proportion to the square of the inlet velocity.
Q. How do you decide whether to us a gravity system or a pumped system?
In most cases it is obvious which system is to be used. However it will be necessary to carry out detail hydraulic calculations to assess if a gravity system is appropriate. The headloss at the inlet to a Grit-Cleanse™ is 1.81m above the centreline of the inlet pipe at the design flow of 20 l/s and there is a free discharge at the inlet to a Series 3 Classifier.
Q. Can the Grit King® process be used for other applications other than at sewage treatment inlet works?
Yes. We would request that the client provides a grading curve and a specific gravity for the material to be separated and this would provide the information for our Research and Development department to size the unit. If the material is colloidal or very fine then vortex separation may not be appropriate.
Q. What is the smallest below-ground internals-only installation that a submersible pump will fit into?
In the UK we ensure that the minimum diameter of the grit pot is 900mm so that a wet well submersible pump will fit. The diameter of the Grit King® separator with this grit pot size is 2.10m.
Q. What dictates the height and position of the anti-siphon valve on the pump feed to the classifier?
There are two reasons for raising the feed pipe above Top Water Level (TWL) in the separator. Firstly to control the flow and secondly to prevent siphoning. A detailed hydraulic calculation is required to calculate the hydraulics and size the pump.
Q. What materials are used for the construction?
In the UK Stainless Steel 304 or 316 is used although other materials could be utilised.
Q. What is the effect of flows higher or lower than peak design flow on the performance of the separator?
The unit will accept higher or lower hydraulic flows than the peak design flow however if the flow is higher than the design flow then the headloss will increase and the performance reduce. If flows are very low then organics will settle out with the grit.
Q. When do you recommend using a Grit-Cleanse™ classifier and not a Series 3 Classifier?
If the ratio of Peak Design Flow to Dry Weather Flow (DWF) is greater than 3 to 1 we recommend the use of a Grit-Cleanse™ Classifier and not the Series 3 Classifier. This is to enable the grit entrained sewage to be put through a secondary separation stage prior to the classifier archimedean screw thus reducing faecal organics discharged in the grit.
Q. Do you use the spray bar provided on the classifier above the archimedean screw for grit washing?
Although there is a grit spray bar provided on the Series 3 Classifier it is not connected to a water supply as standard. We do connect the spray bar on the Grit-Cleanse™ to a potable or washwater main as standard.
Q. Do you require access to the top of the Grit King® separator?
There are no moving parts at the top of the separator and therefore access is not required at high level for routine maintenance.
Q. Is the system able to operate on unscreened sewage?
We recommend that the Grit King® process is operated after screens as in our experience the influent at a sewage works can contain very large objects. Also, if we are operating with a pumped system, rag balling can create a problem. Depending on the specific circumstances, we would consider installing upstream of screens but this would not be our preferred option.
Q. Does the system ever block?
It is important that the recommended control philosophy is followed and under these circumstances blockage problems are unlikely. If the control system is switched off for a prolonged period with flow continuing to run through the separator, then grit will continue to be collected in the grit pot and could build up to a level where it would be difficult to mobilise again. It is therefore important to be able to isolate the separator when the process control is switched off. Hydro do offer a bolted hatch to the bottom grit pot at an additional cost.
Q. You offer water or air backwash within Grit King® Separator. Which is preferable?
Either. The decision will depend on the availability and cost of water on site. Some sites have remote inlet works without a close water supply and in this case the supply of an airset may be preferable to providing a new water supply.