Controlling two valves with different flow-rates to achieve mixing

[kdv1988]

Guys,
I hope you guys are keeping well.

I have been working on developing a Compact Dispensing Station for my CNC Machine & Parts Washer where coolant is mixed with water in different concentrations & volumes as per the requirement which will vary on a day-to-day basis (not the concentration, but the volume).

My design consists of two lines with valves & Flow meters, one for coolant (pumped from a barrel/drum) and the other for water (coming directly from the plant's water supply pipes). Concentration of coolant required is in the range of 1-3% for top-up of sump & liquid volumes(mixed) required will be different everyday, as per the losses in the CNC sump. But normal range I am expecting would be around 50 Litres +- 10/20%

My system consists of a Direct Acting Solenoid Valve followed by a Flow-meter which detects liquid flow-rate & sends signal to the PLC to shut-off the valve when desired flow is met. This is in both the lines (coolant & water).

Now since a 2% coolant for 50Litres would mean approx. 1 Litre of coolant in 49 Litres of water, how do I control the flow of both the liquids so that I achieve homogeneous mixture through-out. I cannot run both the liquids together cause then how would I meter the flow of coolant to match the flow of water?

I do not have space for another tank where I can drop both these liquids and achieve mixing.

I am using this as reference -

https://youtu.be/hFZgbdoZbSI

(Skip to 4:10 in the video).

Any help will be appreciated.
Thanks,
KV

 

[1503-44]

Solenoid valves are typically just on/off. Not good for controling flowrate. Use a globe or plug valve to control water flow and run a chemical injector pump to control the coolant flow rate into the water. Make the injection downstream of the flow meter, which will only measure the water flow. You will be able to control the flow of coolant via the pump speed, so you'll then know the flow of each fluid making up the mixed stream.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[Compositepro]

That mixing station takes as much space as another drum. It does have a computer on it which seems to appeal to young people.

 

[kdv1988]

@Compositepro
This does not really help. This system is not just to appeal to young people. Post COVID, companies will want to automate certain mundane tasks such as maintaining coolant levels in a sump.

 

[kdv1988]

@ax1e, I am not looking to control the flow-rate using Solenoid Valves. The flow-sensors will detect the amount of liquid that has flown through the valve and then shut it when the desired flow has been met.

Could you explain which type of chemical injector pump you are referring to? Peristaltic , positive displacement , gear pumps etc?

I need a pump that can suck the coolant from as much as 10' away.

 

[1503-44]

You can use almost any type of (I would recommend a positive displacement) pump, as long as it has some form of controllable speed accurate enough to keep the flow of coolant within the tolerance you want. Problem is that they can get pricey very fast and you do not mention any target flow rate, only a volume of 50 liters and I don't know if that is 50L per second, a minute or 50L per day, so I must leave the selection up to you. I'm sure most will have the capacity to deliver 10ft, as long as you don't buy an aquarium pump and the pipe diameter is reasonable. Search Google for "[chemical] injection pumps", "dosing" and "additive pumps". Looks like these might work, although I never heard of them before and they are centrifugal. I have heard of Grayco. Select 50psi (lowest they have) and click the button, give them a call.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[kdv1988]

@ax1e, There are 2 conditions where I need a pum :-
1. First is top-up where approximately 1-3% of coolant in approx. 50 Litres of water i.e 500ml - 1500ml of coolant.
2. Secondly is a full re-fill where approximately 6-8% of coolant in approx. 400 Litres of water i.e 20-32 Litres of coolant.

I do not have any limitation as to the time it should take to pump that much liquid in both cases, although the entire process of feeding the mixed liquid to the tank shouldn't go beyond say 8-10 minutes. This is debatable, but that is the range I am looking at.

I need the suction capacity to be 10ft, and not the delivery. For eg, the pump will be mounted on my Dispenser with the drum approx 6' away. Add to that the 3' height of the drum and you have a suction of approx. 10 feet.

 

[1503-44]

Pump suction is very much dependent on the vapor pressure of the pumped liquid (ie more difficult with propanes and bottled gas, hot gasoline, boiling water), high temperature, near boiling liquids, and the vertical heights involved, while somewhat less on horizontal length, as long as your pipe diameter is reasonable. With your low flow rates (+/- 10 gpm) and pumping mostly water, probably not near boiling, right?; things should be OK. You can discuss those specifics with the pump vendors. It might be better in certain high temperature, high vapor pressure situations to reverse the tank and pump locations, even if it requires doubling the discharge pipe lengths, but I think you'll be fine here. If you have a very high vapor pressure coolant, or boiling water, call me back.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[LittleInch]

kdv

Going back to the start - You state
"I cannot run both the liquids together..." and
"I do not have space for another tank where I can drop both these liquids and achieve mixing"

Well you will have to choose one or the other.

Your range of flow rates / percents is quite high at 1 to 8% min to max.

I was looking to see if there were flow driven mixing turbines and there are, but most seem to be about 2-3% mixing max

BTW your lift capacity is only 10 ft if the drum is 6 feet underneath your mixing station, not 6 feet "away"

Thee are many mixing and injection pump set ups which inject set amounts which you can vary by a display setting or manually.

Or you can do it like the video man does, but he seems to be flowing one chemical then the water and just jetting it into the bucket to mix it. If you can create a swirl or mixing current inside the vessel then the timed or metered solenoid valves might do the trick. But you need to resolve the first points I made above.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

2 control valves may not be required if you have 2 small pd pumps (one for each stream) whose flow per stroke is only minimally affected by viscosity. Then it would be just a matter of adjusting the speed of the concentrate pump ( in relation to the speed of the diluent pump) to get the desired mix ratio. Use an inline static mixer on the mix stream to homogenise.