itscoldoutside
New Member
Posts:19
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| 13 Oct 2018 05:06 PM |
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Closed loop hydronic radiant floor system heated by brass heat exchanger. Static pressure is 8 psi. When the system runs the pressure gauge drops to 0. Is that normal?
The Tee for the Gauge is about 6" from the intake side of the pump. The T is connected to a 3" pipe, then an elbow, then 3" of pipe to the gauge. |
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sailawayrb
Veteran Member
Posts:2272
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| 13 Oct 2018 05:27 PM |
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No, low pressure (less than about 1 psi) at the pump inlet is indicative of pump cavitation and the system should not be operated this way. Does the pump sound noisy like it is pumping a pebble/water mixture? Static pressure for residential HR systems is typically something like 15-20 psi. The goal is to keep the pressure at the pump inlet sufficiently above the vapor pressure of the fluid so air bubbles don't form causing cavitation which can be destructive to the pump impeller. |
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Dana1
Senior Member
Posts:6991
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| 13 Oct 2018 05:32 PM |
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A drop of 8psi is equivalent to about 19 feet of pumping head, which implies you have a high head pump &/or a lot of flow restriction along the path, with very little flow.
Does it work?
To keep the system from potentially drawing in air into the isolated loop run it at a pressure where it's always at least ~3psi on the intake side of the pump while the pump is running. |
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Dana1
Senior Member
Posts:6991
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| 13 Oct 2018 05:35 PM |
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If it's caviating (possible, even likely-thanks sailawayrb!) you should be able to hear it, and would be able to hear it stop when the pressure is high enough to prevent it. |
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sailawayrb
Veteran Member
Posts:2272
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| 13 Oct 2018 05:40 PM |
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Thanks Dana and your restriction thought sounds probable. Perhaps there is some valve partially closed that shouldn't be or some other physical restriction. It could also be that the system has a slow leak and gradually lost pressure. Getting the pressure at the inlet above about 1 psi (water vapor pressure at about 100F) should stop the cavitation, but having the pressure at the inlet be a couple more psi higher than this would be the goal (not have cavitation and not over pressurize the system). |
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itscoldoutside
New Member
Posts:19
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| 13 Oct 2018 08:55 PM |
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System is working. There is a small amount of noise form the pump. For the first diagnostic step should I add water to the loop to get the pressure up to 15 psi? I doubt I can do it without introducing some air but in theory the air eliminator should take care of that. |
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sailawayrb
Veteran Member
Posts:2272
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| 13 Oct 2018 09:30 PM |
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Yes, you need to add more water to increase the pressure. Not being familiar with your system design, I can’t advise the easiest way to accomplish that. Perhaps you have a valve that is connected to your domestic cold water plumbing that you can just crack open and then quickly close to get the pressure you need without over-pressurizing your system. Some systems have a device like this to automatically maintain the desired system pressure: Combination Feed/Backflow Valve |
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itscoldoutside
New Member
Posts:19
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| 13 Oct 2018 09:39 PM |
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Unfortunately the system is not connected to the water supply. I can only add water via a hose bib. I can connect that to the spout on nearby utility sink. I suppose I can fill the hose with water before connecting to minimize air introduced into the system. |
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sailawayrb
Veteran Member
Posts:2272
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| 14 Oct 2018 12:56 AM |
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Well, if you have purge valves, it really wouldn’t be a bad idea to just properly flush and purge your system. However, if you are not comfortable doing that, don’t do it now as you don’t want to get caught in cold weather with an inoperative HR system and risk freezing the plumbing. |
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thescottcav
New Member
Posts:46
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| 14 Oct 2018 01:25 AM |
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Is there a system drain near the fill? What about your manifolds? If you get a 5 gallon bucket and a utility pump you can add water and purge via the bucket. This is how I fill and purge our glycol loop for the garages. |
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itscoldoutside
New Member
Posts:19
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| 14 Oct 2018 02:47 PM |
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I don't think I should risk purging the system right now. If I introduce air during the fill to increase pressure will the air eliminator take care of it? |
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sailawayrb
Veteran Member
Posts:2272
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| 14 Oct 2018 04:01 PM |
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If you don't introduce too much air, you should be fine. The risk would be creating an air lock somewhere in system that prevents proper circulation. Using the bucket and pump approach suggested by thescottcav would be preferable and less risky than using a long hose. |
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arkie6
Veteran Member
Posts:1453
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| 14 Oct 2018 10:48 PM |
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Posted By itscoldoutside on 13 Oct 2018 09:39 PM
Unfortunately the system is not connected to the water supply. I can only add water via a hose bib. I can connect that to the spout on nearby utility sink. I suppose I can fill the hose with water before connecting to minimize air introduced into the system.
Is the elevation of the sink faucet higher than the system fill connection? Does the fill connection have an isolation valve? If so, get or make a garden hose the correct length without any loops. Tightly connect hose to system fill connection. Very loosely connect hose to sink faucet. Now gradually open faucet valve to fill hose and allow air to escape from the loose connection. Once the air is out of the hose and only water escapes from the loose connection, tighten the hose connection at the sink. Now crack open the system fill connection isolation valve while monitoring pressure and close when you reach desired pressure. This method should introduce little if any air. |
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itscoldoutside
New Member
Posts:19
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| 14 Oct 2018 11:16 PM |
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Posted By arkie6 on 14 Oct 2018 10:48 PM
Is the elevation of the sink faucet higher than the system fill connection? Does the fill connection have an isolation valve?
The sink is about 2' higher than the fill valve. What is an isolation valve?
Mine has a vertical pipe with a hose bibb then a ball valve then another hose bibb.
Do I close the ball valve and then add water to the lower hose bibb? |
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sailawayrb
Veteran Member
Posts:2272
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| 14 Oct 2018 11:51 PM |
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Something like this: Webstone |
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arkie6
Veteran Member
Posts:1453
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| 15 Oct 2018 08:50 AM |
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Posted By itscoldoutside on 14 Oct 2018 11:16 PM
Posted By arkie6 on 14 Oct 2018 10:48 PM
Is the elevation of the sink faucet higher than the system fill connection? Does the fill connection have an isolation valve?
The sink is about 2' higher than the fill valve. What is an isolation valve?
Mine has a vertical pipe with a hose bibb then a ball valve then another hose bibb.
Do I close the ball valve and then add water to the lower hose bibb?
A ball valve is a type of isolation valve.
I am going to assume that the line connecting to the radiant heat system is at the bottom of this configuration, then a hose bibb, then the ball valve, then another hose bibb at the top. Or looking at it from the opposite direction top-to-bottom: hose bibb, ball valve, hose bibb, radiant heat system fill line.
If that is correct, then do the following:
1. Close the ball valve if not already closed.
2. Connect the garden hose to the UPPER hose bibb.
2a. Route hose back to sink maintaining a gradual rise so that no big dips or loops exist to trap air in the hose.
3. Loosely connect hose at sink. 4. Slowly fill the hose and get all of the air out at the high point back at the sink. You may want to mechanically agitate the hose to insure any air works its way up to the high point.
5. Tighten hose connection at sink after all of the air is out of the line. 6. Keep the faucet or valve open at the sink to maintain pressure on the hose.
7. Now slightly open the ball valve to allow the higher water pressure from the sink to raise the pressure in the radiant system. 8. When radiant system pressure reaches desired pressure, close the ball valve. 9. Close faucet back at sink, then put a catch pan or bucket under hose end at fill line hose bibb to catch any remaining water when you disconnect the hose.
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itscoldoutside
New Member
Posts:19
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| 16 Oct 2018 03:35 PM |
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I am going to assume that the line connecting to the radiant heat system is at the bottom of this configuration, then a hose bibb, then the ball valve, then another hose bibb at the top.
It's a closed loop that is heated via a heat exchanger plate. The bottom hose bibb connects to the tubing that heats the floors, the top hose bibb connects to a pipe that runs into the heat transfer plate. |
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sailawayrb
Veteran Member
Posts:2272
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| 16 Oct 2018 03:55 PM |
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All HR systems are closed loop and pressurized. However, it would now appear that you have two closed loops, each on a different side of a heat exchanger. Presumably the loop with the low pressure at the pump inlet is the bottom hose bib that connects to the tubing that heats the floors. If so, that’s the one that needs additional water/pressure. Do you know what the pressure is in the other loop, presumably the boiler loop? Why do you need a heat exchanger? Is the boiler heating your domestic water too? A sketch of the plumbing would be more than helpful... |
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itscoldoutside
New Member
Posts:19
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| 17 Oct 2018 08:05 PM |
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There are 2 loops connected by a heat exchanger.
Loop 1: heated by a mini boiler and supplemented by a a gravity fed solar heating tank. The pressure in this loop is OK.
Loop 2: heated by the heat exchanger connected to Loop 1. This is the loop that needs more pressure.
Is this correct?
Close the ball valve on Loop 2. Then connect a hose to the bottom hose bibb and to the spout in the utility sink with a loose connection so air can escape. After the hose is filled with water slowly open the hose bibb valve to pressurize the loop. After that run the system with all 4 zones open which will probably lower the pressure. If that happens repeat until there is at least 3 psi when the loop pump is running. |
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sailawayrb
Veteran Member
Posts:2272
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| 17 Oct 2018 11:14 PM |
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Yes, that should work fine. |
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