How to install dosing pumps and more in the AWE Spring 2016 Watermark
pH Correction Skids
We often get enquiries for pH correction skids. One particular customer had purchased an industrial washing machine and which used a heated alkali solution for cleaning.
After the washing and rinse cycle, the wastewater was discharged. This discharge fell outside of the customers agreed consent to discharge agreement. Unfortunately for our customer - the supplier of the industrial washing machine did not see this as their problem, and did not wish to help.
We designed and built an all polypropylene skid mounted unit with a GRP corrosion resistant control panel. The whole system was supplied ready, wired and tested.
The pH correction system worked on a batching principal. Waiting until a high level was reached before starting the recirculation pump and acid dosing pump, which is controlled by a pH control loop.
When the pH is within limits a valve opens allowing the neutralised solution to flow to drain. At a low level in the tank the pump stops waiting for the tank to fill to a high level again. In combination this allowed us to design and build a simple and cost effective system to neutralise small volumes of effluent requiring pH correction; for which our customer was very thankful!
Black Dosing Pumps - The "A" Series
The range of our Black Electronic Dosing Pumps has been extended to include the A+ series which offer increased outputs, while remaining in the same compact housing as our C+ series of black electronic dosing pumps.
There are 5 pumps in the A+ Series ranging from 0 - 1.6 L/Hr against 17 Bar (that's 250 PSI) to 0 - 9.3 L/Hr against 3.3 Bar pressure.
As standard the wetted parts are PVC head, Teflon diaphragm and seals with ceramic ball valves. There is the option of either PVDF or 316 Stainless Steel being available for an additional cost.
The A+ Series features a manually adjustable stroke length and either manual or automatically adjustable stroke frequency - i.e. the number of strokes the pump makes per minute. This gives the user a very wide turndown ratio of the pump output.
If the external pacing option is selected, then the control of the pump output frequency (the number of strokes the pump makes per minute) will be controlled by PFM (pulse frequency modulation). The pump will make one stroke for each volt contact closure (or pulse) that the pump receives. The dose rate can then be adjusted over a 10:1 ratio b means of adjusting the pump stroke length.
The external pacing control is usually from either a water meter or the PFM output from one of our pH controllers - models P7685 and MO5-pH.
Our A+ pumps feature metric sized hoses making them easier to install as replacements for existing pumps.
Please note not all manufacturers use the same sizes of metric tubing our A+ pumps. The A+ series use 6 x 8 mm as this offer a lower resistance to flow and allows a higher viscosity solution to be pumped.
Dosing Pump Installation - Technical Tips 💡
We have been supplying dosing pumps for over 30 years with many regular customers who keep coming back to us, we are told that this is because of technical advice, back up and ex-stock deliveries.
We recently had a customer who purchased some of dosing pumps and timers - for what is a simple and regular application.
Our customer had requested a dose rate of 18 - 20 litres per hour so we had recommended our AT4 series of electronic pumps, which are with the larger 12mm OD LDPE dosing hose as standard, rather than the AT3 series, which has the 6mm OD LDPE tubing.
We then received a call from the customer who said, "The dosing pump is not pumping the chemical, nothing is coming out of the injection fitting, and the chemical container is full"
After some questions it transpired the chemical reagent has an SG of 1.6, the dosing run is 30 metres long - None of this is a problem for the AT4 series of dosing pump - so we were puzzled as to his problem.
We weren't told that the suction from the chemical container to the position of the dosing pump was in excess of 10 metres!
Dosing pumps have a very good delivery - in excess of 15 Bar on some models (Over 20 in our E+ series of black dosing pump).
A dosing pump with an output of 15 Bar is the equivalent of dosing water 150 metres in the air (in our customers case where the SG is 1.6 - it is the equivalent of dosing this 93.75 metres into the air).
The suction capabilities of small dosing pumps are limited to 1.0 - 1.5 metres - depending upon the model. So the pump must be mounted close to the chemical container, and flooded suction installation is always a good idea if the environment allows.
For the customer, he was unable to mount the pump outside close to the chemical container. One option would be for the customer would be to install a smaller chemical day tank and the dosing point closer to the point of use and have a transfer pump controlled by a level controller to pump from the bulk storage tank outside to the day tank. The transfer pump could be a cost effective double diaphragm pneumatic pump.
For this installation the customer kept the dosing pumps to use for another application and purchased one of our Big Wheel Peristaltic pumps the BWP120 with Viton tubes. We tested this at our works in Stafford and it proved cable of meeting the customers requirements due to the duty cycle and nature of operation.
Our recommendations are to always keep your pump suction as short as possible and adhere to the manufacturers specification for installation - and we've produced a handy guide to help with the installation of dosing pumps:-
This was the installation which our customer installed with a long suction to a peristaltic pump mounted below the liquid level in the IBC.
We do not recommend this installation type. The pump should be installed adjacent to the chemical and above the reagent level so that the chemical is drawn into the pump via a suction lift.
Peristaltic pump tubing is a consumable item which normally splits at the end of its working life, so we strongly recommend positioning the pump so it cannot syphon or leak out of the contents of the chemical IBC.
Short Suction - Long Delivery
This is a better installation as a dosing pump is used with a flooded suction - so there is no problem in priming the pump.
Diaphragm dosing pumps generally have a poor suction but good delivery pressure depending upon the model selected. We recommend the chemical container be bunded - the pump fitted into a polypropylene housing, and the dosing tube to be double confined.
Bulk Tank and Day Tank
For installations where the chemical is stored outside or some considerable distance away from the point at which it is required; the installation of a day tank and transfer pump with level controller is a better installation.
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