Notebook 3 : How do I install a dosing or metering pump?
Although not generally the most expensive part of the overall project or installation the dosing pump is central to the on going successful production of a quality end product. For example in a number of cases water quality is paramount for a number of applications, and can be treated with as many as 15 chemicals to meet this wide array of uses.
Poorly installed dosing pumps and dosing systems become a source of on-going irritation and unnecessary expense and inevitably leads to the equipment being criticised, rejected and eventually replaced with something else all of which is totally unnecessary and costly, and avoidable if the initial selection and installation is done correctly. A lot of poor installations are carried out by third party contractors focused on cost reduction at the expense of long term reliability, and in some cases with a total lack of understanding or appreciation of the importance of the task at hand. Basic requirements for a sound dosing pump installation include mounting the pump so that it is accessible, particularly the wet end which requires access for maintenance of diaphragms and occasionally for non-return valve cleaning and service. Valves must be mounted vertically with the pressure or output valve on top and the suction or input valve at the bottom and the location should be vibration free.
Installation with (external) relief valve
It is also important to allow access to the manual stroke adjustment so that the micrometer scale is able to be read. Mounting the pump at a convenient height so that it is easy to maintain is also sensible, as is a clean environment and a properly piped installation will not have media all over the floor. Many installations are supplied pre-packaged by leading suppliers, incorporating the pump and all accessories in a cabinet or mounted on a back frame so that all that needs to be carried out on site is to have the suction and delivery lines connected.
Pre-packaged dosing plant offer the advantage that they are checked and tested before leaving the works making it easy to rectify mistakes before the plant is shipped to site.
Dosing pumps by virtue of their diaphragm design are leakage free so any spillage is usually due to diaphragm failure or poor pipe work. Diaphragms are expected to provide 7000 to 10000 hours operation and early failure detection is possible by fitting a diaphragm rupture detection device which will also prevent unnecessary spillage.
It is important to select piping with the correct material compatibility and size. The pipe inside diameter [ID] must be the same or larger than the bore of the valves on the dosing pump. Connection between the pump valves and piping is usually the weak point of the installation and needs to receive special consideration. Leading manufacturers are able to supply connection adapters to suit the design engineers requirements, however this requirement should be clearly specified early on in the pump purchase request.
Piping considerations need to also take into account the capacity of the pump and the fitting of pulsation dampeners as this can have a significant impact on pipe size and cost.
Installation of a Pulsation Dampner
All piping should be installed in such a way as to prevent any stress on the pump valves and pump head. Flexible lines are recommended, especially on plastic head pumps, as in the example of PVDF valves and pump head used for dosing 300 l/h of 98% sulphuric acid at 3 bar delivery head. Undue strain could lead to breakage or leakage with serious consequences. All piping on the supply or input side to be kept as short as possible and this can also be larger than the output or delivery side which will assist in satisfying the NPSHr requirements. An example of these valves is shown below:
Double Valves, GFK type
The sealing method used on dosing pump valves is the 0-ring or compression packing type. This highly effective method of sealing relies on the basic principles of elastomers, namely memory, the ability to store energy, deformability and high bulk modules or incompressibility.
Joints using this method can be hand tightened to operating pressure and excessive installation force is not recommended. The correct connection adaptors are always available from the pump supplier and MUST be used. Due to the method use in this type of joint there is always more force available to seal than to allow leakage.
Notebook 1 : “What is a dosing or metering pump.?”
Notebook 2 : “How do I select a dosing pump?”
Notebook 3 : “How do I install a dosing or metering pump?”
Notebook 4 : “What does a complete dosing pump installation look like?”
Notebook 5 : Continues the discussion on liquid dosing technology.
If you have any questions please go to liquiddosing@dosetech.co.za
Pumps
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