Timer connected to water heater?

[relliott]

Originally Posted by mlarson

Follow the yellow line. There is no open loop on the cold side.

But Mike the pump is creating pressure in the tank as there is no imaginary pipe inside the tank as you drew in your diagram.

If the tank fills with lets say 5 pounds more pressure (ok do not know specs) then would not the 5 lb pressure be equally applied to both cold inlet an hot outlet as they both are openings at top.
Why would water choose to follow only the one path?

[Jeffrey R. Jonas]

Cold supply pressure is greater than pressure created by pump, therefore preventing backing up into cold supply.

[Michael R. Boyett]

Originally Posted by tdietrich1

How does a 'passive' one work?

Well, first of all it has a little daisy and happy face painted on the side of it along with a peace symbol. It just very quietly does its thing and seems very meek and mild...probably made in CA, specifically S.F. and likely votes Democrat.

[Jeffrey R. Jonas]

Originally Posted by mboyett

Well, first of all it has a little daisy and happy face painted on the side of it along with a peace symbol. It just very quietly does its thing and seems very meek and mild...probably made in CA, specifically S.F. and likely votes Democrat.

But... is it an Athesist?

[David A. Andersen]

Originally Posted by relliott

The thing I have always had a hard time with is..
Why does the recirculation pump not push hot water back into the cold supply and only push it around the hot water supply pipes if there is no check valve on the cold water side.?

.

Like many other things concerning fluid dynamics, pumps (and fans) do not just pump they suck!

When nothing is turned on the static pressure throughout the system is equal.

Turn on the pump motor and a negative pressure is created in the hot water line.
Hot water flows from the heater down the hot water supply line because it now has a lower pressure than the cold water line.

If you turn on a hot water valve, a lower pressure is created in the hot water supply pipe and hot water from the tank flows towards the valve and cold water enters the hot water tank because it has a higher pressure.

Because the pump is on, that does not mean the pressure on the hot water side is higher than the pressure on the cold water supply. The sucking negative pressure is proportionate to the pumping positive pressure and circulation only occurs in the hot water loop.

[relliott]

Originally Posted by jjonas

Cold supply pressure is greater than pressure created by pump, therefore preventing backing up into cold supply.

Ok
Now I am beginning to grasp the concept.
I assumed that the 40 lb (for visual purpose) pressure is equal at both outlet and inlet but since the pump is not creating say 50 lb pressure it will not fight the incoming water.

In other words only the cold supply is giving resistance. WHACK! to the side of my head.

[David A. Andersen]

Now I am beginning to grasp the concept.

Not yet...

back up one.

[Michael Larson]

Well said David.

[Jeffrey R. Jonas]

Originally Posted by relliott

Ok
Now I am beginning to grasp the concept.
I assumed that the 40 lb (for visual purpose) pressure is equal at both outlet and inlet but since the pump is not creating say 50 lb pressure it will not fight the incoming water.

In other words only the cold supply is giving resistance. WHACK! to the side of my head.

In it's most simplistic form... yes. What David said is right on the money.

[Michael Larson]

Originally Posted by tdietrich1

How does a 'passive' one work?

tom

Via a gravity return line from the farthest fixture.

The cooler water will "sink" toward the water heater.

[relliott]

Originally Posted by dandersen

Like many other things concerning fluid dynamics, pumps (and fans) do not just pump they suck!

When nothing is turned on the static pressure throughout the system is equal.

Turn on the pump motor and a negative pressure is created in the hot water line.
Hot water flows from the heater down the hot water supply line because it now has a lower pressure than the cold water line.

If you turn on a hot water valve, a lower pressure is created in the hot water supply pipe and hot water from the tank flows towards the valve and cold water enters the hot water tank because it has a higher pressure.

Because the pump is on, that does not mean the pressure on the hot water side is higher than the pressure on the cold water supply. The sucking negative pressure is proportionate to the pumping positive pressure and circulation only occurs in the hot water loop.

For some reason I understand what you are saying.

Excellent post for helping me grasp the mysterious process. (not anymore)

very cool (sorry those are the only greenies available)

Knew you were good for more than rainbow pics

[Chuck Evans]

Originally Posted by mlarson

Bob the loop is formed from the hot side of the far fixture back to the cold inlet of the water heater.

The loop is between the hot water outlet and the drain line. Does not involve the cold water inlet.

[David A. Andersen]

Originally Posted by cevans

The loop is between the hot water outlet and the drain line. Does not involve the cold water inlet.

That is how the after market (construction) design gets back.
I misread this also (at first). It takes a kit at the furthest fixture and uses the cold water line as a return.

Not the same as here thought.

[Michael Larson]

Originally Posted by cevans

The loop is between the hot water outlet and the drain line. Does not involve the cold water inlet.

Not true. It either enters the cold inlet at the top which has a dip tube that leads to near the bottom of the tank or the modified drain valve assembly at the bottom.

[Michael R. Boyett]

Here's another recirculation design (note the use of the cold water side & the 'kit" David referred to):