Flow Switch

[Bob O]

Looking for some recommendations for a pulsed rate indicator or flow transducer for a 50/50 mixture of H2O and Glycol. My flow rates exceed 100GPM. I have found some at Omega Engineering but looking for other options and recommendations. Thanks, Bob

[Ron_Smith]

I've been using SIGNET products for flow monitoring for the last 3 or 4 years and haven't had any problems. Signet Systems

[Bob O]

Ron, Thanks for the link. I will look at their products. Bob

[DanW]

If you have a need to measure flow rate, a magmeter will do a great job on water/glycol. Then alarming from the flow signal is no big deal. But magmeters are expensive, compared to flow switches. For flow switches, there are mechanical types. I avoid the very thin stainless steel strip or vane type targets, (like the McDonnell Miller brand or Flotec brand), because the thin strip fatigues and breaks over time, creating problems downstream. The Kobold KAL series has similar mechanical paddle with much more robust target - a piece of metal that stands up very well over time. The switch is a tiny little reed switch though, OK for a low level DI input, but I wouldn't put 110Vac across one. There are piston and shuttle flow switches, but I've never used one. They seem to be more for machinery use than process use. Gems and Dwyer offer a bunch of either, in different materials and different flow ranges. An alternative to mechanical switches are thermal flow switches, which put heat up a small heater in the flow stream and then measure how rapidly the heat is removed from the heated element. It's called thermal dispersion. I've used both IFM Efector and Kobold and see that Dwyer has them now, found both Kobold and IFM suitable for low temperature fluids that don't change temperature rapidly. Both claim to be temperature compensated for changing media temperatures, but reality is that rapid step changes will fool either. The advantage of thermal dispersion is the intrusion is a stainless "knob" that sticks into the pipe, relatively little pressure loss, nothing to break off and float downstream. I've never had a heater element die, have had an occasional electronic controller module fail, but that doesn't involve messing with the plumbing.

[IO_Rack]

We use Gems. http://www.gemssensors.com/

[Bob O]

All, Thanks for the replies and the links. I looked at a three and have narrowed it down to two options at this time, the Signet 3-2540 and the Gems FS-200 Series. I have played with the IFM Efector model but I don't want and external adjustment on the unit. Any opinions on the durability of these two units? http://www.gfsignet.com/products/pdf/2540-41-17spec.pdf http://www.gemssensors.com/SearchSeriesPN.asp?sSearch=fs-200&nQuestionID= Thanks, Bob Edited March 8, 2006 by Bob O

[TConnolly]

Bob, take a look at IFM Efector flow meters. http://www.ifmefector.com We have used these for years with excellent results and reliability. No moving parts.

[gravitar]

Since I work on water-cooled welding equipment, I have my $0.02 I would love to add.. I have had good luck with the ifm efector SI1000, but like you said it does have buttons that curious fingers can play with, which I have seen happen from time to time.. There is a "lockout" function that makes it harder to make innocent mistakes, but someone with a little intelligence and malicious intent can easily get past this. I've seen situations where I would swear this has happened, too! My A-B guy swears they will have a similar sensor "REAL SOON". Of course, he's been telling me that for a couple years now. I wonder what it'll be like, whenever they decide to release it. I also concur with those that dislike the "limit switch" style, like McDonnel Miller and others. No sight glass or LED indicators, so it is a bit harder to tell if you truely don't have flow or if the switch failed. And we've had numerous failures of this style of switch. We've had pretty good luck with the "piston and shuttle" switches (I like this description, I never knew what to call these!) probably because they're SO simply constructed. For those that haven't seen this type, All it is is a clear plastic threaded pipe nipple with a spring-loaded ring magnet inside. The coolant flow forces the magnet off its seat, and a reed/hall effect switch clamped to the outside of the tube closes when the magnet is pushed far enough to be in close proximity with it. VERY simple, yet effective.. Allows visual inspection of flow medium, and I would have to imagine these are really cheap. Perfect for a welder, where all you really care about is whether the water is flowing or not. I've been to one shop where all the welders had an interesting gadged called a "FlowStat" sensor made by Lake Monitors. It has a big sight glass with a visible paddle-wheel inside, and it gives you linear signals for flow AND temperature. It gives me everything I would want.. Visual inspection, flow and temperature. These must be the "Cadillac" of flow sensors... I would have to imagine these are WAY expensive, and for my purposes I don't want to fool with analog inputs when all I need is on/off anyway. As far as things to fiddle with, there is an external trim-pot.. Which I hate because my maintenance guys never seem to know when to STOP TURNING THE STUPID SCREW!!! It does look like there's provisions to put a cover over this part of the housing atleast. If I had an application where I really need to know the RATE of flow, I would give these guys consideration. http://www.lakemonitors.com/

[Bob O]

Alaric and gravitar, Just to make sure I wasn't missing something, I called ifm and ask if they had a unit without the external buttons. No luck. You can lock them but they can also be unlocked just as gravitar mentioned. gravitar I will look into that link later tonight when I get home…I think or I plan Thanks Again, Bob Edited March 8, 2006 by Bob O

[GerryM]

I have used these before with good success. They have a couple of buttons that you may not like. http://www.greatplainsindustries.com/ I depends on your application but generally I have found paddle wheel types suck, unless you set them up for a particular purpose at a small range of flow. They also need alot of straight pipe to make sure the flow profile is correct. The turbine style, see the link above, I have found to be more stable and not too expensive. The ifm efector stuff I have used and like. The best most stable flow I have found, very accurate also, is a magnetic flow meter. They are expensive, so it depends on your application. www.rosemount.com Edited March 9, 2006 by GerryM

[Bob O]

Update I am waiting for a quote from Emerson and since I am on vacation today, I will not see it until Monday. I have a system in place and working but "if" the operators just crack the gate valve to provide enough flow [6-8 GPM] to trip my current flow switch, a Dwyer blade type, they can continue and possibly do damage $$$ to our tooling. Maybe I failed when I accepted the answer for the amount of flow need when originally doing this "just need to know if there is flow or not" Vent I do not mind doing improvements but it gets old when management does not hold their people accountable for simple tasks. End Vent Thanks, Bob Edited March 10, 2006 by Bob O

[Ron_Smith]

Having one of those mornings myself... had to walk all the way across the plant (500,000 sq ft) and wipe a blob of grease off the face of a sensor. The operator knew what was wrong... he just didn't want to work today... thought production would send him home.

[TimWilborne]

Sounds like every Monday and Friday here

[robh]

Yep. I really like it when they ask for MULTIPLE light stacks, alarm banners, and audible alarms to let our operators know that a tank is full. But no matter what it still gets over filled. Can't have it automatically shut off cuz the operator "has to have control" of his system. I keep asking for the money to install shock collars on our operators, but I have yet to find an OSHA approved device!

[TConnolly]

Bob, IFM does have some models that are analog output only. These don't have any switches. Of course however you have to then use an analog input - which adds expense, I use quite a few of the SI-1004 and set the switch points in the PLC.

[Bob O]

Alaric, I check with ifm again and the units without the external buttons will not work in this application. Thanks Again, Bob

[gravitar]

It seems a bit extreme but we've had to mount pressure switches, flow switches, etc. in locking J-boxes to keep people from "adjusting" things that they shouldn't adjust! Just another possible suggestion :)

[Bob O]

It is just crazy to have to go through this. I double check with head of tooling, since it is his equipment, I am protecting, and he is the “customer” and asked if external adjustments would be ok? Does anyone want to guess the answer? The list of possibilities is getting shorter. Thanks, Bob

[Ron_Smith]

Whenever I get stuck with one of those situations I go ahead and quote a package that will do EXACTLY what they want. In your case I could see PLC w/analog I/O - $2,000 Porportional Valve - $850 Flow Meter - $350 HMI - $1800 Misc. - $350 LOT'S of times when I do this the problem that was sooo important yesterday seems to fade away Ron

[TimWilborne]

Don't laugh. I have done this before. The buttons on the IFM are small recessed rubber buttons. Set them, then put super glue in the cavities of the buttons. Then you have a fix flow switch and you will know if someone tampers with it since they will probably be too sorry to clean the mess up and put new glue in them.

[gravitar]

ifm does sell a clear plastic "cap" that goes over the button/display end, maybe this could be glued to the body of the switch? That way it could be cut off for when the sensor really DOES need to be re-taught..

[TimWilborne]

Well I wish you would have informed me of that before I glued the buttons