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Hydraulic Equivalent to GFCI?

Hydraulic Equivalent to GFCI?

Hydraulic Equivalent to GFCI?

(OP)
We are a water utility with an established backflow and cross connection control program. For commercial customers, we require an RP on domestic and irrigation lines, and DCDAs on fire services.

We have someone who wants to use domestic water as a heat source/sink for commercial building HVAC loads, via a double walled heat exchanger with air gap between the walls. The user would take domestic water from the utility system, run it through the heat exchanger, and pump it back to the utility distribution system (for eventual consumption by other users). Our State regulators have approved exactly this installation for another utility.

This plan is completely against our backflow policy. Yet, it’s a potential revenue stream for a non-consumptive use. I’m looking for other’s thoughts about how this could be implemented without undue risk to the water supply.

In particular, it seems to me that if there was a hydraulic equivalent to an electrical GFCI, where the unit would interrupt all flow if the supply and return flow weren’t very nearly the same, then we could be assured the unit was operating without cross connections. Is such a device available? Perhaps users working with high value or high hazard fluids have implemented something similar.

Thanks in advance.

RE: Hydraulic Equivalent to GFCI?

Is the air gap equipped with a leak detector?
E.g. double walled Diesel injection lines for marine use are arranged so that any flow into the gap between the walls is routed to a small chamber with a float switch that shuts the engine down after a few cc have leaked.

Even that is not as reliable as the common system for beverage dispensers, where the beverage is circulated through coils in a tank of ice. The ice in turn is produced in a separate icemaking machine and routed manually or by gravity from the icemaker to the beverage coil. ... the important point is that at no point is there a single or even a double metal wall between the primary refrigerant and the beverage. A double walled heat exchanger does not provide that degree of separation.

It also seems unfair to dump your building's heat load into your neighbor's domestic water supply, which he will then be obliged to cool to get it to the same temperature as it was supplied to you. It's the sort of thing that no one would object to for conditioning a hot-dog stand, but for a multistory office building, that's a whole nother kettle of fish.
Your neighbor's lawyer could get a nice vacation home out of that issue. ... as could yours, whether you win or lose.

Mike Halloran
Pembroke Pines, FL, USA

RE: Hydraulic Equivalent to GFCI?

(OP)
Mike - As far as the heat exchanger itself leaking, I'm not so worried about that - whatever leaks won't make it back into the system. What I am worried about is the potential for cross connection by unauthorized taps of the heat loop within their building.

The heat load's another issue we'll have to face.

Thanks for your help.

RE: Hydraulic Equivalent to GFCI?

To answer your actual original question, no, there's no GFCI equivalent.

There are hydraulic fuses that shut above some predestined flow.

There are also flow dividers, basically gear pumps with their shafts connected, that can force two flows to be equal or pretty close.

I suppose you could instrument the shaft of a flow divider to trigger a shutoff above some limiting torque value suggesting a difference in flow. It's the sort of thing you could do with relative ease and not too much development cost, in an oil hydraulic system.

In a domestic water system, you could burn a fortune in development and maybe have nothing to show for it. Water powered hydraulics appears pretty regularly in the technical press, usually with a lot of hopeful prose and a bucket of Navy money, and then it gets real quiet. Some of the modern poly- unobtainium- sulphide plastics have performed impressively in recent gestations, but they are still mostly unaffordable in useful sizes.

Mike Halloran
Pembroke Pines, FL, USA

RE: Hydraulic Equivalent to GFCI?

What you describe is in essence similar to a pipeline leak detection system, what goes in should come out. There are a few ways of doing this, but the most basic is still a variance on temperature corrected volume in and out sending an alarm. You probably have a steady flow and no branches so many of the issues which affect pipeline systems aren't there, but so long as you have a couple of decent straight lengths in and out then a turbine or UT meter will allow you to monitor this via a simple plc which can be tuned and alarm or shutoff if some determined discrepancy in flow is found. This is how it's done on pipelines as it's not a standard thing so there's no ready made box. Given that you will have a temp difference in and our then you should go for corrected, standard volume to compare not just actual.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

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