Thermostat?

[Jim Robinson]

This device is new to me. It is on the output side of the domestic hot water. I think it is some type of temperature limiting device, but there is no mixing valve. Anyone familiar with it?

[Jerry Peck]

It's a flow gauge.

I measures the water flow in gallons per minute.

When I worked at a defense plant right after high school where we made electron tubs for the military, the larger tubes used in battleships for their radar were water cooled - I tested them setting the gallons per minute for the cooling and the gallons per minute for the RF load, that with the temperatures of the two provided a measurement of the power output (around 5 megawatts output).

The ones I used were about 2 feet long and much larger in diameter.

Also ... :) ... that says "gpm" on the side of it. :D

Also ... looks like it is installed upside down, rather, with the flow in the wrong direction for the gauge. The water flow direction should be the direction the arrow is pointing.

Added with edit: Is the water flowing down or up in the photo? If "down", then the gauge would be installed in the correct orientation with the flow - that close-up does not show the piping to verify which way the water is flowing.

Some of those gauges are designed and intended to be installed vertically "up" only (all the ones I used were designed and intended to be installed vertically "up" - but that does not mean there are not others which are designed to be installed horizontally or vertically "down", just would be a different design as they would not be using 'gravity' for part of the resistance, they may use a spring (which weakens over time) or some other means to resist the flow and thus be able to reliably measure the flow.

[Jim Robinson]

Water was flowing down, so that part looks correct. Wonder why they would want a flow gauge on the hot water line? Who knows.

[Jerry Peck]

Water was flowing down, so that part looks correct. Wonder why they would want a flow gauge on the hot water line? Who knows.

Except for the part I was typing and adding with edit while you were posting (I took a phone call part way through my typing, that slowed my posting the edit part down):

Added with edit: Is the water flowing down or up in the photo? If "down", then the gauge would be installed in the correct orientation with the flow - that close-up does not show the piping to verify which way the water is flowing.

Some of those gauges are designed and intended to be installed vertically "up" only (all the ones I used were designed and intended to be installed vertically "up" - but that does not mean there are not others which are designed to be installed horizontally or vertically "down", just would be a different design as they would not be using 'gravity' for part of the resistance, they may use a spring (which weakens over time) or some other means to resist the flow and thus be able to reliably measure the flow.

[Jerry Peck]

This one has a spring inside of it, so it could be used in various orientations:
Hedland H621-010 EZ-View Flowmeter, Polysulfone, For Use With Water, 1.0 - 10 gpm Flow Range, 1" NPT Male: Science Lab Flowmeters: Amazon.com: Industrial & Scientific (http://www.amazon.com/Hedland-H621-010-EZ-View-Flowmeter-Polysulfone/dp/B005K2MP06/ref=lp_3206433011_1_14?s=industrial&ie=UTF8&qid=1431816656&sr=1-14)

Why someone would want a flowmeter there? I can only think that they were measuring the flow of various fixtures for whatever reason they wanted that information for????

The one in your photo does not measure very much flow, so if everything was being used, I can see that maxing out and not providing a reliable measurement.

[Robert Dalga]

This one has a spring inside of it, so it could be used in various orientations:
Hedland H621-010 EZ-View Flowmeter, Polysulfone, For Use With Water, 1.0 - 10 gpm Flow Range, 1" NPT Male: Science Lab Flowmeters: Amazon.com: Industrial & Scientific (http://www.amazon.com/Hedland-H621-010-EZ-View-Flowmeter-Polysulfone/dp/B005K2MP06/ref=lp_3206433011_1_14?s=industrial&ie=UTF8&qid=1431816656&sr=1-14)

Why someone would want a flowmeter there? I can only think that they were measuring the flow of various fixtures for whatever reason they wanted that information for????

The one in your photo does not measure very much flow, so if everything was being used, I can see that maxing out and not providing a reliable measurement.

It's possible that was a 'recirc' line with a pump. This would also explain why it looks like it was installed upside down.

[Dwight Doane]

It's a flow gauge.

I measures the water flow in gallons per minute.

When I worked at a defense plant right after high school where we made electron tubs for the military, the larger tubes used in battleships for their radar were water cooled - I tested them setting the gallons per minute for the cooling and the gallons per minute for the RF load, that with the temperatures of the two provided a measurement of the power output (around 5 megawatts output).

The ones I used were about 2 feet long and much larger in diameter.

Also ... :) ... that says "gpm" on the side of it. :D

Also ... looks like it is installed upside down, rather, with the flow in the wrong direction for the gauge. The water flow direction should be the direction the arrow is pointing.

Added with edit: Is the water flowing down or up in the photo? If "down", then the gauge would be installed in the correct orientation with the flow - that close-up does not show the piping to verify which way the water is flowing.

Some of those gauges are designed and intended to be installed vertically "up" only (all the ones I used were designed and intended to be installed vertically "up" - but that does not mean there are not others which are designed to be installed horizontally or vertically "down", just would be a different design as they would not be using 'gravity' for part of the resistance, they may use a spring (which weakens over time) or some other means to resist the flow and thus be able to reliably measure the flow.

I think your very close Jerry but if you look below the sight glass there is an adjustment screw and this is used to control the maximum flow - (I suspect and engineer with girls ) After having my nieces from Puerto Rico visited my last year I can understand why one might want to put one of these on the hot water heater :p . The main reason I might want to put one on is to keep the flow low enough as to not over draw the water heater (limit the demand to the output capacity_

My Brother in law has another solution to this problem - Small electric water heater on timer (push the button and you get 10 minutes of hot water (Electricity on the island is about $0.40 a KW - the girls thought it was so nice to have unlimited hot water they would take 2 hour showers when they were here.

I have also used these on large refrigeration systems to control the flow of refrigerant to the expansion valve

[Jerry Peck]

I think your very close Jerry but if you look below the sight glass there is an adjustment screw and this is used to control the maximum flow

I saw that adjustment and thought that it was an adjustment for calibration of the device (I guess the calibrating technician in me came out ... having worked in the Standards Lab at a defense plant right after high school where I calibrated oscilloscopes, voltmeters, signal generators and all kinds of other things). :)