Specifying Accessories for a Metering Pump

How do we specify the piping accessories required when specifying a metering pump? We have prepared the following list to help you make appropriate choices that will satisfy the needs of your application.

In our previous blog articles on specifying a metering pump we stressed the importance of matching the liquid to be pumped with wetted end materials of construction that can safely and economically handle the liquid.  We also discussed the electrical drive motor options for a metering pump.  Here are some thoughts to take into consideration as you are specifying accessories for a metering pump:

• What can accessories do for the pumping system?  A pulsation dampener can smooth out the flow of the liquid and eliminate pressure spikes.  A pressure relief valve can prevent damage to a pump or piping when an over pressure event occurs.  A back pressure valve can improve pumping repeatability.  And a calibration column can help the pump operator precisely measure the pump output once it is put into service.  Let’s take a look at each element.
• Pulsation dampener: this device consists of a small vessel with a diaphragm dividing the upper and lower part of the chamber.  Air pressure in the upper section dampens the pressure and flow spike that normally comes with a diaphragm type metering pump.  Elimination of up to 95% of the spike is achievable.  Madden MF Series and JN Series pumps use 10 cubic inch pulsation dampener models, and the MH Series pumps use 36 cubic inch capacity models.  The important element in specifying pulsation dampeners is to make sure the diaphragm and body are compatible with the liquid to be pumped.  Many installations function just fine without a pulsation dampener, but if a smooth injection rate and constant pump discharge pressure are important, for example in a sprayer nozzle application, then including a pulsation dampener can be vital to the performance of the pumping system.  We sell the Blacoh Fluid Control pulsation dampeners which we have found to be economical and reliable in use with Madden metering pumps.
• Pressure relief valve: helping to protect the pump, pump motor, and discharge piping is the job of the pressure relief valve.  When the set pressure is reached the pressure relief valve opens and permits a flow of the liquid to a safety containment, protecting the pump and the piping from damage.  We use adjustable Griffco Valve diaphragm type pressure relief valves.  The important factors to specify are the pressure rating, flow rate range, the materials of construction, and the size of the piping connection.  The adjustable valves will offer an adjustment range, for example from 10-150 psi, and the customer can set the pop off level with an adjustment screw.  The pressure relief valves automatically reseal when the excess pressure subsides.
• Back pressure valve: like the Griffco pressure relief valves, the Griffco diaphragm type back pressure valves are adjustable.   The back pressure valve provides an artificial constant pressure for the pump on the discharge side, and that constant pressure improves the flow control repeatable accuracy of the pump.   This is important when there is virtually no pressure on the discharge side, or where the system pressure will be changing from time to time.  Constant back pressure against the pump improves the performance of the pump by making the discharge flow rate more consistent and controllable.  Another use for the back pressure valves is to prevent siphoning of the liquid from the supply tank through the pump when the suction head is higher than the pump discharge head.  Again, the important factors to specify are the pressure rating, flow rate range, the materials of construction, and the size of the piping connection.  In addition, back pressure valves are normally used in conjunction with pulsation dampeners to improve the performance of the dampener.
• Calibration column: this is a clear PVC or glass tube marked with calibrations used to enable the pump operator to precisely determine the flow rate of the metering pump.  The tube is normally installed in the suction piping between the pump and the supply tank.  The calibration column is filled from the supply tank, and then the tank is isolated from the pump with valves, and the pump is operated using the supply of liquid in the calibration column.  Using a stop watch and recording the amount of liquid pumped over a short period of time the pump operator can create a pump curve that will show the pumping rate at various pump adjustment settings.  The columns come in various capacity sizes for use with different pump capacities.  To size a calibration column we select a unit that will hold a minimum liquid volume equal to the maximum pump flow rate for one minute.  In addition to specifying the liquid volume capacity of the calibration column it is important to select tube and fitting material that will be compatible with the liquid being pumped.

Those are the factors to consider when specifying  accessories for a metering pump.  For more information on the accessories click on this link.  For additional help in specifying a metering pump for your  application, consult the Madden Pump Selection Guide on our website, call us, or send us an email inquiry.  We are always quick to respond.