Small flow Metering pump or solenoid valve


Thread Starter

Ken Emmons Jr.


I'm looking for an industrial metering pump (Peristaltic) that can be
used to dispense fluid for a machine. I want something that runs off of 24VDC with a remote on/off via a 24VDC NPN output and that is
preferably packaged for industrial applications, not the typical
laboratory bench top setups you tend to see a lot of.

Alternatively if anyone has suggestions for a solenoid valve that can
dispense microliter amounts of Kerosene or lightweight machine oil that would be appreciated.

Any ideas?

I think you are approaching the problem from the wrong end. You need to specify the process characteristics more and will probably have to live with whatever packaging and interface you can find.

Is it more important to dispense at a specific rate or to dispense a specific volume? What accuracy do you need? Are you mixing it with another fluid? Are you spraying through a nozzle? Does the nozzle need "suck back"? Do you need to vary the volume from time to time? How will the operator make adjustments? Etc., etc.

I'm going to take a guess based on no real information and suggest that you look at Nordson or Graco dispensing valves. Find the local reps and talk to them about the application. In dispensing applications interfacing the dispenser with your control system is usually the least of your worries.

Ken Emmons Jr.

Reply to M. Griffin,

Thanks for the input. The process characteristics aren't that critical in this case, but I see your point about needing more input to make a recommendation. We just need a light flow to ooze out onto a surface and coat a metal piece with a thin film of light forming oil or kerosene. We will be making our own end tooling to control the outlet characteristics onto our piece so that it flows/wicks properly, etc.

A peristaltic pump was chosen by someone else at my company to continually pump fluid out onto our metal piece. The pump came from a industrial distributor that didn't provide the brand name or detailed specifications so I was leary. It also had exposed knobs that I didn't like since we want this to be a "set and forget" kind of application. Perhaps we can mechanically fix the knobs with setscrews. The reason for having industrial packaging is such that we can mount it to the side of our machine since there is no horizontal surface on this machine to set a "lab bench" type of unit. I have not purchased pumps before so I am looking to see if there is an industry leader for very low flow rate pumps for industrial use. Our intended flow would max out at something like 500-1000 microliters per second and the pump will need to be turned off if the machine stops. The accuracy needed is minimal and could be as bad as +/- 50%.

I also thought that the peristaltic pump was a bit overkill so I was
looking into solenoid valves that can handle this fluid. Perhaps I
should just look as SMC and Festo and see if they have a fluid valve
that fits this application and use gravity feed (or very low pressure) to create a gentle pulse of oil/kerosene triggered by the machine controller at the appropriate point in the cycle.

Thank you,

I think your best bet would be to use a standard pressure pot (ie, you put a tub of this material directly into a chamber which is pressurised albeit at low pressure) and then feed it to an end effector. Needle valves will be best to allow a small amout of fluid through at a time, but you need to be careful what type of seals you use. If you are definitely using Kerosene then Buna_N or Teflon will be good, and standard nitrile rubber will be a disaster. If you control the valve via a solenoid then it should be all you really need.

I can give you all the advice you want on pumps, if you wish, but the control is all up to you.

Good luck
Or, you could just contact the distributors for the two brands I suggested (Graco, Nordson). They sell pneumatically operated dispensing valves for all sorts of fluids.

Dispensing valves come in two basic types. There are "flow" type valves and positive displacement valves. The "flow" valves simply open and allow a fluid to flow. The flow rate is usually adjustable via a precision needle valve. The positive displacement valves have a piston with an adjustable stroke. The piston pumps out a set amount of fluid. The return stroke can often be set so that it "sucks back" some of the fluid so that it doesn't drip at the nozzle.

Both of these are usually fed through a "pressure pot" (so are the peristaltic pumps). The pressure pot is a pressurised container in which you put a jug of fluid. The air pressure forces the fluid out through a line to the dispensing valve. The pressure pots come in various sizes. You will need to add a reliable sensor to sense fluid level so the operator will know when the level is getting low.

With a typical application, you have the following:

- A pressure pot with a jug of fluid inside.
- A plastic fluid feed line running from the pressure pot to the dispensing valve.
- A dispensing valve.
- A pneumatic line from the dispensing valve to a small pneumatic valve (usually just one in a convenient valve bank). Sometimes you want an in-line regulator on this so you can run the dispensing valve at a lower pressure.
- Some programming in the PLC to turn on the valve as required.

The peristaltic pump might sound like overkill, but in a lot of applications people need to be able to make regular fine adjustments while the machine is running. The biggest problem is usually that temperature changes over the course of the day (especially in the summer) can change the viscosity of the fluid. You might need more or less fluid according to how its viscosity affects how it flows over the part.

You're not going to be able to set the dispense amount to *exactly* what is required. The problem with "too little" is obvious, but "too much" can be a big problem as well. The biggest problem with "too much" fluid is that in a lot of applications this can create a mess as the excess gradually accumulates over the course of a shift. Whether or not this is a problem depends on your process and machine design.

Something else you'll need to keep in mind in dispensing applications is that flushing out the lines is a routine operation, so you need to make that simple to do.