Inner Workings of a Instant Hot Water Dispenser

[George7941]

I tok apart a Westinghouse WH1500C Instant Hot Water Dispenser. My question is regarding the expansion tank which sits on top of the stainless steel tank where the water is heated and specifically - how does the expansion tank retain its charge of air and ensure that the air does not dissolve into the water flowing through the tank?

The brown fitting shown in the pic is the inlet fitting to the main (stainless steel) tank bringing in cold water. The expansion tank ties into this fitting through a side port on the fitting. There is a restrictive orifice in the fitting just downstream of this port.

My best guess as to how it all works - the orifice creates some pressure buildup in the incoming water and forces some water into the expansion tank. The expansion tank is normally at atmospheric pressure plus few inches of water column. This fresh cold water in the expansion tank releases some dissolved air when it warms up and this supply of air, albeit small, is enough to maintain the air charge in the expansion tank.

 

[bullwinkle]

I would think it has a bladder to separate air & water, like all the bigger ones (for water heaters, well systems, etc.

 

[George7941]

It does not have a bladder, I separated the two halves of the main stainless steel tank

 

[mk378]

It looks like the clear gasket is also a diaphragm separating the tank into a water section and an air section.

 

[SHOZ]

If it gets the water to boiling temp the air will come out, the first time.

Fast Facts: Boiling Water Bubbles​

• Initially, the bubbles in boiling water are air bubbles.
• Bubbles in water brought to a rolling boil consist of water vapor.
• If you reboil water, bubbles may not form. This can lead to explosive boiling!
• Bubbles form in other liquids, too. The first bubbles consist of air, followed by the vapor phase of the solvent.

 

[George7941]

It looks like the clear gasket is also a diaphragm separating the tank into a water section and an air section.

Yes. But the upper half is not airtight, it has a vent hole which can be seen in the first pic.
The main tank has no bladder, as seen in second pic.

Now my guess becomes - there is no air cushion, the flex of the silicone diaphragm provides space for expansion as the water is heated in the main tank. Without the expansion, the dispenser tap would keep dripping during the heating of the water.

If it gets the water to boiling temp the air will come out, the first time.

Fast Facts: Boiling Water Bubbles​

• Initially, the bubbles in boiling water are air bubbles.
• Bubbles in water brought to a rolling boil consist of water vapor.
• If you reboil water, bubbles may not form. This can lead to explosive boiling!
• Bubbles form in other liquids, too. The first bubbles consist of air, followed by the vapor phase of the solvent.

 

[George7941]

If it gets the water to boiling temp the air will come out, the first time.

​

Not sure what you mean by "the first time", but, yes, as I posted in my original post, the air will come out as the water is being heated. Though I was referring to the small amount of water in the expansion tank. Any air generated in the main tank would just vent out through the tap as soon as it is generated.

 

[George7941]

I would think it has a bladder to separate air & water, like all the bigger ones (for water heaters, well systems, etc.

Those have an air tight air half of the tank so that it has a pressurized air cushion.