What is the initial pressure of the hot water diaphragm vessel

Question

What initial pressure should be set in the diaphragm vessel for a 120l gas water heater.
The hydrophore system works in the range of 1.5 - 3.7 bar.
The installer left the factory set pressure Refix DE - 4 bar

W0jtek92 · Answer

Why change your pressure?

Skwantowany · Answer

And what is the diaphragm vessel for in hot water? The diaphragm vessel is installed in closed central heating systems, where water circulates in a closed circuit.

saskia · Answer

It can be, but it would be better if the pre-pressure was at least a quarter of a bar below the max. network pressure.
One main reason is the damping of hydraulic clatter when the valves close.
If the diaphragm does not have pressure pressure over its larger surface, then its operation takes place with a delay, ie it only partially eliminates hydraulic knocks, and the compensatory operation is also slow and only with a significant increase in pressure.
such a vessel should work similarly to a CO vessel and be about 1/4-1/3 filled with water.

Skwantowany · Answer

OK, but if the pressure is variable in the network, as stated by the author of the post, even twice, then the vessel may have a pressure value greater than the pressure in the network at the moment and thus does not fulfill its role. if it was possible to maintain the pressure in the system at a certain level, then the vessel would do its job.

saskia · Answer

Consider the fact that at low pressures (lower pressure range) hydraulic knocking is unlikely to occur.

Skwantowany · Answer

This is a quarter of a bar (+ a little) below the pressure of the vessel, this vessel will not work. In that case, you would need to specify a min. the pressure at which knocks occur and the vessel should only work from this pressure.

saskia · Answer

This would be the best solution, but here we are limited by the capacity of the vessel.
If we reduce the initial pressure in the vessel too much, then with large pressure fluctuations in the network, it may happen that the vessel has too low initial pressure and with increased pressure in the network is completely filled with water, which will not meet the basic protection as an expansion vessel protecting against pressure increase, e.g. in the boiler, and then the safety valve will have to work, and this should rather be avoided, because that's what the expansion tank is for :-)

This quarter of a bar lower initial pressure, it only gives additional use of the vessel to eliminate hydraulic knocks, while maintaining the basic tasks of the vessel, but it will not eliminate them in the entire pressure range.

robert45 · Answer

As I wrote, the pressure is variable, because it is a hydrophore installation (own water intake).
The measurement of the pressure in the vessel after filling the installation with water showed 4.5 bar, regardless of the pressure and temperature of the water. I lowered it to 3.5 bar. I probably did it incorrectly, because without draining the water from the vessel. I assumed (I do not know if right) that if the vessel pressure was higher than the water pressure in the system (max. 3.7 bar), then the vessel does not fulfill its function.
Reflex recommends setting the pre-pressure in this vessel to the lowest water pressure in the system.
I thought that the purpose of the diaphragm vessel, apart from water hammers, is the comfort of using several water intake points without loss of pressure.
This was the case before the vessel was installed. Simultaneous drawing of hot water caused a significant drop in pressure, and thus the comfort of use (e.g. from the shower) was unsatisfactory.

saskia · Answer

The diaphragm vessel is not a hydrophore and will not supplement pressure drops, but it can only prevent too much pressure increase after changing the temperature of the water in the boiler.
By setting the pre-pressure slightly below the system pressure, it can also eliminate heavy hydraulic clatter by absorbing (smoothing) abrupt changes in pressure and flow.

The initial pressure is set before connecting the tank to the system, i.e. when there is no pressure in the system (pressure = 0). The pressure measurement of the network should be made at the same level of the system where the diaphragm (compensation) tank is installed.

William Bonawentura · Answer

A complete tank protection system includes: pressure reducer or pressure switch on the cold water supply, check valve, diaphragm vessel approved for contact with drinking water (white) safety valve at the outlet of the storage tank.

robert45 · Answer

After changing the pressure in the vessel, the installation works without water hammer.

serwisant73 · Answer

Weird question....

pan_kotek · Answer

I will join the topic.
What is the difference in the location of the safety valve:
1) at the cold water inlet to the hot water tank
2) at the outlet of hot water from the tank

I understand that the difference is in the temperature of what will flow out.

robert45 · Answer

The installation is working properly. The change in the initial pressure in the vessel did not adversely affect the operation of the system. Thank you for your comments. Topic to be closed.

What is the initial pressure of the hot water diaphragm vessel

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