Recommendations on the thresholds of the relay pressure water systems of individual houses
Denote Pnps – lower threshold in pressure pumps (bar), the upper threshold Rvps-pressure pump is switched off (bar).
The difference thresholds Rvps-Pnps determines the amount of water issued accumulators supply systems. The greater this difference, the more efficiently the accumulator, but the disc is loaded with more and may rupture.
Rvkl value (the pressure of the pump) is determined from the value of hydrostatic pressure (water height) in the Boilermate system of your home. For example, if the height of the pipes in your system is 10 meters, then the pressure of the water column is 10 meters, which equals the pressure of 1 bar.
What should be the minimum pressure Pnps? The air pressure in the chamber-pressure expansion tank must be equal to hydrostatic pressure, that is, in our case a bar. The lower threshold Pnps, then must be slightly larger (0.2 bar) air pressure in the expansion tank.
However, we need the Boilermate to work stably. The most critical from the standpoint of stability, is the highest point of the analysis (such as tap or shower on the top floor). Crane is working properly, if the pressure drop in there for at least 0.5 bar. Hence the pressure must be 0.5 bar plus the hydrostatic pressure of this point. Thus, the minimum gas pressure in the Amtrol CH-41BZ Boilermate is equal to 0.5 bar, plus the reduced value of the hydrostatic pressure in the expansion tank at the location (distance in height between the lowest point and the point of parsing the location of the accumulator). In our case, if the accumulator is at the lowest point of water, the minimum value of gas in it should be assigned a bar + 0.5 bar = 1.5 bar, and the threshold (turn) of the pump Pnps = 1.5 + 0.2 = 1.7 bar. If the Amtrol WH-41Z Boilermate is located at the top, and a pressure sensor at the bottom of the system, the gas pressure in the accumulator should be set 0.5 bar, while the threshold of the pump Pnps = 1.7 bar.
In appointing the upper threshold of the automatic water Pvps to consider a few things, first and foremost characteristic of pressure pump. The value of the pressure created by the pump and expressed in meters of water column, divided by 10, will show maximum pressure. However, please note that:
- In the characteristics of the pump are the maximum settings without taking into account the hydraulic resistance of pipelines;
- Voltage electrical network often does not correspond to the nominal value of 220;
- Pressure at maximum flow the pump is minimal, and your system will be filled with a very long time;
- In continuous operation characteristics of the pump decreases.
With this in mind, we recommend to assign the value of the upper threshold is 30% lower than the maximum pressure of your pump.
However, in determining the initial upper threshold is the height of your house, or rather the height of the water supply at home.
The value of upper threshold is the height of the water system, expressed in meters plus 20 meters, and divided by 10. You get pressure expressed in bars.
In a domestic water supply is usually recommended to appoint the difference between the lower and upper threshold 1.0 – 1.2 bar. This is the most appropriate value.
Thus, to determine the upper limit of the pressure of the pump, we recommend:
a) define the lower threshold pressure of the pump;
b) to the resulting value added 1.2 bar;
c) compare this value with the pressure characteristics of the pump. It should be 30% lower than the maximum pressure of your pump. So you can check your pump selection.

Facts about Boilermate (other name Indirect Water Heater).

This reservoir served a dual function – a safety valve pressure caused by temperature changes and supply point for the new water with natural losses in its hardware. This type of installations created many problems caused by oxygen received through an open container and constantly circulating with water. The evaporation of water, it is not timely substitution also increased the percentage of dissolved salts, which cause the formation of scale, especially in small diameter PEX pipes, radiators, boilers and reduced the effectiveness of the system.

Installing an open vessel at the highest point building assumed that the tank will be placed directly under the roof of the house ie in the most vulnerable to changes in temperature and location, thus, remained a possibility of freezing water contained in the tank during the inactivity of the unit itself.
Corrosion and rapid scale formation in pipes, boilers and radiators forced the owners to the continuous maintenance of installations and replacement units.
For these reasons, almost a century reigned undisputed advantage for the production of cast iron boilers and radiators for rust resistance.
The evolution of materials, reduction of prices of production and installation, additional equipment, the use of Taco circulation pumps and smaller in size but more efficient boilers – have reduced the diameter PEX pipe.
Improving the quality of the production of heating systems clouded the old concept of open systems, the oxidation products continually harmed equipment.
The transition to closed systems. The solution was to completely close the system and find an acceptable way to accommodate the volume changes due to, the natural expansion of the water temperature increases.

Fifty years ago, went on sale first expansion tanks equipped with a diaphragm.
This type of tanks that are still being made, decided two main problems:
a) Compensation for expansion warmed water;
b) Excluding the possibility of contact of water with oxygen in the air.

This significant result was achieved by a simple manufacturing of metal tank, which consists of two parts, separated by a sealed diaphragm made of rubber. One of the two parts could be filled with compressed air, the other part is connected with the flow of the free circulation of hot water heating system.
Until now, the majority of heating systems is assumed that the hot water from the boiler circulates around the perimeter of the scheme, and the tank is located at the highest point of the structure. Mains supply the radiators, where the water gives off heat, warming the environment. Chilled water was out of the radiator from its lowest point, going down the secondary range of circulation of the heating system. Under this scheme, water is returned to the boiler to be warmed again and start a new cycle.

The ability to change the internal pressure of the system allowed to place radiators on an arbitrary height, with very low material costs, reducing the need for a long and fruitless pipelines that would lead to significant heat losses, or would require significant cost to their insulation.

Possibility to create a heating system under pressure allow greatly simplifies their design, allowing you to apply the optimal solutions as a cost for the equipment, and the time of installation.

Summarizing, we can say that the Expansion tank with a diaphragm was a necessary decision to produce more efficient energy-saving and less costly in terms of installing the heating system.

Current situation

Tanks with a diaphragm made in large quantities, and to this day, the simple design allows you to maintain a more cost-effective prices, in comparison with other, more modern expansion tanks with a replacement membrane.
Their disadvantage is the need to replace the entire tank in case of damage to the membrane.
In USA, due to difficulties in supplying the internal membranes, are in high demand and used by even the expansion tanks understated dimensions.