Hot water pressure and hot water accumulator tank


 

Thomas,

On your SM the hot water pressure accumulator tank was originally located between the water heater and the port side of the engine room.

Unfortunately, I have seen some owners remove this tank when it starts leaking. I assume they feel that there is no harm, but actually, they are over-pressurizing the hot water side of their freshwater system. This can cause many issues. If you no longer have the Amel-installed accumulator tank for the hot water system, you should install a 4-8 liter accumulator tank. It is normally connected to the hot water system via a hose from the freshwater manifold which is mounted on the aft bulkhead of the engine room. See photo below and note red circle on the hose.
image.png
Also see an image of a page from my Amel Book, attached.

Best,

CW Bill Rouse
720 Winnie St
Galveston Island, TX 77550
+1(832) 380-4970



On Sun, Jul 14, 2019 at 9:20 AM Thomas Kleman <lorient422@...> wrote:
Bill- I definitely have no accumulator tank in the circuit. I just thought all these years that the basic 40 had a relief valve set too low (7 bar ?). These relief valves tend to last me 1-2 years (I buy them in bulk). Can you send me a pic of the correct setup ? I've never seen one.

Thomas Kleman
SM2K 422 L'ORIENT
Panama


Thomas Kleman
 

Bill- thanks as always for the great info. So this tank is just an 8 liter reservoir for my basic 40 ? Does it only allow ingress under some kind of pressure ?  If not it merely expands my basic 40 into a basic 48, I suppose the additional 20 pct capacity prevents my pressure relief valve from tripping ?


 

Thomas, the purpose of the hot water accumulator tank is to take care of the increased pressure in the hot water system caused by heating the water. Heating water increases the pressure in a closed system and increased pressure can harm components. The accumulator does not increase the storage of hot water.

Best,

CW Bill Rouse
720 Winnie St
Galveston Island, TX 77550
+1(832) 380-4970



On Sun, Jul 14, 2019 at 11:13 AM Thomas Kleman <lorient422@...> wrote:
Bill- thanks as always for the great info. So this tank is just an 8 liter reservoir for my basic 40 ? Does it only allow ingress under some kind of pressure ?  If not it merely expands my basic 40 into a basic 48, I suppose the additional 20 pct capacity prevents my pressure relief valve from tripping ?


Craig Briggs
 

Thomas,
Although Bill correctly points out the expansion tank takes care of the increased pressure, it may be helpful for you to know how it does that so you understand that it's not extra water storage. Picture the expansion tank as a small tank having a rubber diaphragm across the middle (although there are some other designs). It has water on one side and air on the other. As your pump works it forces water into the water end and that forces the diaphragm to flex into the air side until it compresses the air to the pressure that turns off your pump. The next time you run water that pressurized air pushes back the diaphragm, the pump comes on and the cycle repeats.  Hence you will notice the pump will not go off as soon as you close your faucet - it needs a couple of seconds to pressurize the system up to the shut off pressure.

Now, when your hot water heater operates the hot water expands and needs a place to go or it will either open the pressure relief valve or burst the tank. That's where the expansion tank comes in. The expanded water flows back into the system and the expansion tank diaphragm will expand to accommodate it, keeping the pressure in the system below the level of your safety pressure relief valve on the hot water heater. 

Depending on what tank you buy, some are pre-pressurized and some have a schrader (bicycle) valve you use to add air. You'll want to keep the pressure about the same as the cut off pressure of your pump. You can play with it if your pump cycles too long after shutting off the faucet (too much pressure) or if it cycles exactly with the faucet (too little pressure, such that it's just acting as an additional tank with no expansion capability.)

Hope that helps.
Craig