Why a membrane vessel is preferable to a diaphragm vessel

Varem  has carried out a series of tests in its laboratories to test the operation of its vessels for pumping systems and compare them with other products on the market.

In particular, it carried out a series of parallel tests on vessels with balloon membrane and with diaphragm membrane, which offered proof of the significant superiority of the first solution, used by Varem, in given conditions and also drew attention to the limitations of the second solution.

Membrane Vessel	Diaphragm Vessel

The test carried out was the EN13831 cycle test indicated in the Directive PED 97/23/EC, which provides for correct operation of the product for 50,000 cycles at an average temperature of 30°C.

Naturally, one of the most important aspects for determining correct operation of an expansion vessel is the complete discharge of the water contained, for the whole duration of the test. Therefore, we carried out the tests also paying close attention to this aspect, monitoring the performances of the two products being compared in two situations: with pump shut down at 3 bar and at 5 bar.

Case 1: shut down pressure of 3 bar

At a pump shut down pressure of 3 bar, the expansion vessel is filled with a usable volume of water equivalent to 25% of the nominal value. By way of example, a tank with a nominal value of 100 l contains 25 l of water. In this configuration, comparison between the two types of tank showed that the test was passed without any problem.

Case 2: shut down pressure of 5 bar

At a pump shut down pressure of 5 bar, the expansion vessel is filled with a usable volume of water equivalent to 50% of the nominal value. By way of example, a tank with a nominal value of 100 l contains 50 l of water. In this configuration, comparison between the two types of tank showed a significant reduction in the discharge capacity of the diaphragm vessel, which starting from 4000 cycles was measured as 20%. In the case of the 100 l tank, the usable volume of water discharged decreased from the 50 l expected to 40 l.

Analysis of the tanks at the end of the 50,000 test cycles brought to light the reasons for this abnormal reaction of the diaphragm vessel.

The solution with shut down pressure of 5 bar caused yielding of the diaphragm membrane in the fastening area, as shown in the images below:

In fact, this area is subjected to increased stress as the pressure inside the vessel increases, contrary to membrane vessels in which the pressure is spread evenly over the whole of the surface of the membrane.

As a direct consequence of this, the diaphragm behaves abnormally, as indicated in the sequence of images below:

The rubber stretches until it blocks the water inlet/outlet before adhering fully to the inner walls of the vessel, retaining 20% of the usable volume of water inside the vessel.

This situation creates two negative consequences for operation of the system:

1. Increased electricity consumption 
   A reduction in the usable volume of water discharged causes a directly proportional increase in number of pump start-ups and consequently an increase in electricity consumption 
2. Decreased water quality
   The presence of 20% of water retained inside the vessel, causing the problem of incorrect circulation of liquid with substantial stagnation, has the direct consequence of reducing the quality of water in systems used for sanitary water, as well as exposure to the risk of Legionella.

Therefore, we conclude that in systems with pressures in excess of 3 bar, the use of membrane vessels is highly recommended. 

WATER LINE VERTICAL

• Vertical multifunction water tanks
• Replaceable membrane
• Available with galvanised or painted flange
• Red color
• Pre charge pressure 2 bar

LS-LSV

INTERVAREM LS CE -10 + 99 °C

Item Std. Code. Capacity Max. pressure Connection Dimensions Packaging Qty/ pallet     it bar inch mm m3 n. LS 5 S2005361CS000000 5 8 1’ 160x332 0.010 210 LS 8* S2008361CS000000 8 8 1’ 200x348 0.015 144 LS 12* S2012361CS000000 12 8 1’ 270x308 0.024 72 LS 19* S2019361CS000000 19 8 1’ 270x421 0.031 63 LS 20* S2020361CS000000 20 10 1’ 250x500 0.038 56 LS 24* S2024361CS000000 24 8 1’ 351x348 0.045 54 LS 25* S2025361CS000000 25 8 1’ 290x480 0.041 63 LS 40* S2040361CS000000 40 10 1’ 320x587 0.066 36

MAXIVAREM LS CE -10 + 99 °C

Item Std.Code Capacity Max. pressure Connection Dimensions Packaging Qty/ pallet     it bar inch mm m3 n. LS V 50 US050361CS000000 50 10 1’ 379x759 0.126 15 LS V 60 US060361CS000000 60 10 1’ 379x815 0.131 15 LS V 80 US080361CS000000 80 10 1’ 450x789 0.170 15 LS V 100 US100361CS000000 100 10 1’ 450x910 0.200 15 LS V 150 US150461CS000000 150 10 1’1/2 554x1020 0.340 8 LS V 200 US200461CS000000 200 10 1’1/2 554x1213 0.407 8 LS V 300 US300461CS000000 300 10 1’1/2 624x1373 0.596 6 LS V 500 US500461CS000000 500 10 1’1/2 775x1460 1.300 1 LS V 750** US750461CS000000 750 10 1’1/2 786x1925 2 1 LS V 1000** USN10H61CS000000 1000 10 2’ 933x1912 2.200 1 LS V 2000** USN20H61CS000000 2000 10 2’ 1280x2241 2.500 1

LS H 

INTERVAREM - MAXIVAREM LS CE -10 + 99 °C

Item Std. Code Capacity Max. pressure Connection Dimensions Packaging Qty/ pallet     it bar inch mm m3 n. HORIZONTAL LS H 19* S2H19361CS0BP000 19 8 1’ 270x421 0.031 63 LS H 20* S2H20361CS0BP000 20 10 1’ 250x500 0.038 56 LS H 40 US041361CS000000 40 10 1’ 320x587 0.066 36 LS H 50 US051361CS000000 50 10 1’ 379x759 0.126 15 LS H 60 US061361CS000000 60 10 1’ 379x815 0.131 15 LS H 80 US081361CS000000 80 10 1’ 450x789 0.170 15 LS H 100 US101361CS000000 100 10 1’ 450x910 0.200 15 LS H 200 US201461CS000000 200 10 1’1/2 554x1213 0.407 8 LS H 300 US301461CS000000 300 10 1’1/2 624x1373 0.596 6

LSP – LS PV

PLUSVAREM -10 + 99 °C

Item Std. Code Capacity Max. pressure Connection Dimensions Packaging Qty/ pallet     it bar inch mm m3 n. HIGH PRESSURE LS P 8 S5008361CS000000 8 16 1’ 160x332 0.015 144 LS P 20 S5020361CS000000 20 16 1’ 250x509 0.038 56 LS PV 50 S5050361CS000000 50 16 1’ 379x759 0.128 15 LS PV 80 S5080361CS000000 80 16 1’ 453x789 0.170 15 LS PV 100 S5100361CS000000 100 16 1’ 453x915 0.200 15 LS PV 200 S5200461CS000000 200 16 1’1/2 556x1218 0.407 8 LS PV 300** S5300461CS0CE000 300 14 1’1/2 626x1373 0.596 6 LS PV 500** S5500461CS0CE000 500 12 1’1/2 777x1457 1.300 1 LS PV 750*** S5750461CS000000 750 16 1’1/2 786x1925 2 1 LS PV 1000*** S5N10H61CS000000 1000 16 2’ 933x1912 2.200 1

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