Fitters notes |
Thermostatic expansion valves |
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Contents Page
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Superheat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Subcooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 External pressure equalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Charges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Universal charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
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.6 |
MOP charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
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. 6 |
MOP ballast charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
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.7 |
Thermostatic expansion valve selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. . .9 |
Orifice assembly replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
10 |
Danfoss product range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 11 |
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 |
DKRCC.PF.000.G1.02 / 520H1459 |
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<![endif]>Thermostatic valves expansion
Notes
DKRCC.PF.000.G1.02 / 520H1459 |
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 |
Fitters notes |
Thermostatic expansion valves |
Introduction |
A thermostatic expansion valve is built up around |
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a thermostatic element (1) separated from the |
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valve body by a diaphragm. |
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A capillary tube connects the element to a bulb |
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(2) and a valve body with valve seat (3) and a |
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spring (4). |
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A thermostatic expansion valve works like this: |
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The function of a thermostatic expansion valve is |
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determined by three fundamental pressures: |
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P1: Bulb pressure which acts on the upper |
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surface of the diaphragm, in the valve |
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opening direction. |
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P2: Evaporating pressure which acts on the |
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underside of the diaphragm, in the valve |
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closing direction. |
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P3: Spring pressure which also acts on the |
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underside of the diaphragm, in the valve |
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closing direction. |
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When the expansion valve regulates, balance is |
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created between bulb pressure on one side of the |
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diaphragm and evaporating pressure plus spring |
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force on the other side. |
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The spring is used to set superheat. |
Ad0-0001
Superheat |
Superheat is measured at the point where the |
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bulb is located on the suction line and is the |
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difference between the temperature at the |
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bulb and the evaporating pressure/evaporating |
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temperature at the same point. |
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Superheat is measured in Kelvin (K) and is used as |
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a signal to regulate liquid injection through the |
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expansion valve. |
Ad0-0012
Subcooling |
Subcooling is defined as the difference between |
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condensing pressure/temperature and liquid |
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temperature at the expansion valve inlet. |
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Subcooling is measured in Kelvin (K). |
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Subcooling of the refrigerant is necessary to |
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avoid vapour bubbles in the refrigerant ahead of |
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the expansion valve. |
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Vapour bubbles in the refrigerant reduce capacity |
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in the expansion valve and thereby reduce liquid |
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supply to the evaporator. |
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Subcooling of 4 5K is adequate in most cases. |
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Ad0-0015 |
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© Danfoss A/S (AC-DSL/MWA), 10 - 2006 |
DKRCC.PF.000.G1.02 / 520H1459 |
<![endif]>Thermostatic valves expansion
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