Dosing Systems

[ivanhoe374]

I was just wondering what people's thoughts/experience was in regards to the having or not having back pressure valves and pressure relief valves in small dosing systems (3.5 - 130L/hr)

The Alldos pumps i am planning on using have there own shut off system in the event of high pressure (why have the pressure relief valve?) and the injection fittings provide "enough" back pressure for the pumps to operate accurately.

I guess from an engineering prospective it is a good idea to have all these items, as well as pulsation damperners and calibration cylinders, however from an economic point of view (and when trying to win jobs!) these items are not always included.

Any thoughts? experiences?

 

[m777182]

I was supposed to dose continuously in a range 0,5 l/h to 3,5 l/h into a pilot reactor equiped with a aggitator, at the beginning at constant rate but later in a feedback control loop. A lab piston pump was available with an input for frequency controlled flow.
The problem I was faced to was how to measure such a flow with a liquid that was saturated with small bubbles of air.
The second problem was that the reacting mixture should not enter back to the line and the third problem was how to distribute my solution evenly into the reactor.
I put the outflow from the line as near to the tip of the aggitator as possible and to prevent self suction from the line I made a small valve at the end of it, that opened at ~0,2bar overpressure.
To smooth pulsation I used a flow equalizer and a capillare.There was an option of a computer averaging flow readings over selected time interval too. There was of course a safety release valve there to prevent any accident.
The system was initialy not designed so complex but at the end it provided a flow with ~1-2% ripples.
m777182

 

[bimr]

Back pressure valves are designed to enhance the performance of chemical feed systems by applying a continuous back pressure to the chemical feed pump, while also acting as an anti-syphon valve.

If you are not pumping into a pressure system, you do not need them.

The cost of these valves has to be less than $100. Don't see how that much money is going to lose a project for you.