Thermal Expansion Valve Function
温度式膨張弁 (short called “TXV” ) is one basic system components for refrigeration cycle. His functions as follow:
1. Throttle and pressure reduction
Throttle and reduce pressure of normal temperature and high pressure liquid refrigerant after condensation in the condenser, adjust the refrigerant which flows through the evaporator, and control the overheat at the evaporator outlet. Overheat = air outlet temperature – 蒸発温度.
2. Regulate flow
According to the temperature signal obtained by the temperature sensor, TXV can automatically adjust the refrigerant flow entering the evaporator to adapt the changes of refrigeration load.
3. Prevent abnormal overheating
The expansion valve adjusts the flow rate to make the evaporator keep a certain overheat, ensure the effective use of the evaporator, meanwhile avoid liquid 冷媒 entering the compressor to cause liquid strike; 同時に, it can prevent abnormal overheating.
TXV Classification and Installation
TXV can divide into two types: internal balanced and external balanced.
Internal balanced TXV
Temperature sensor pressure = spring pressure + evaporator inlet pressure. Valve diaphragm pressure comes from evaporator inlet.
External balanced TXV
temperature sensor pressure = spring pressure + evaporator outlet pressure. Valve diaphragm pressure comes from evaporator outlet, always used in systems with large evaporator resistance.
TXV 構造
Install temperature sensor onto the horizontal air-outlet pipe at the evaporator outlet, 1.5m away from the compressor suction port. Temperature sensor mustn’t place on the pipeline with accumulated liquid. そしてパイプにしっかりと巻き付けます, その間、金属の自然な色を露出させるために、接触部分の酸化スケールをきれいにします。.
エア出口パイプ径＜25mmの場合, 温度センサーはパイプの上部に取り付けることができます; 直径＞25mmの場合, 空気出口パイプの下側で 45° で結ぶことができ、パイプ底部の油の蓄積が温度センサーの性能に適切な影響を与えるのを防ぎます。.
温度センサーの設置
TXVデバッグ
通常の状態で TXV をデバッグする必要がある 冷凍 動作状態. 流量が多すぎる場合, デバッグネジを時計回りに半回転回します. さもないと, デバッグネジを反時計回りに回します, それも半回転. デバッグネジは一度に半回転以上回さないでください.
以上の間隔が必要です 15 minutes between each debug.
TXV overheat should be 5~8℃. If not, adjust it.
TXV Debug Example
故障: A constant temperature and humidity エアコン is running with both compressors, air outlet is 22.5℃, air inlet is 16.8℃, its cooling performance is not good. Freon was sufficient, and filter not blocked.
検査: 2 コンプレッサー’ air outlet was overheated and temperature at the expansion valve outlet was low. The evaporator outlet temperature was 18℃, and air outlet pressure was 3.2kg/cm2 (the corresponding temperature was -5℃, overheat was 23℃), which was obviously deviated from the normal overheat. Reason is the expansion valve wasn’t open enough.
Debug: After correct debug, the evaporator outlet temperature was 12℃, air outlet pressure was 4.8kg/cm2, the corresponding temperature was 4.5℃, and the overheat was 7.5℃.
The specific data before and after the on-site debug are as follows:
| アイテム | Evaporator outlet Temp (℃) | Compressor air outlet pressure (kg/cm2) | Ralated temp for Compressor air outlet pressure(℃) | Overheat(℃) | Overheat meet the request or not |
|---|---|---|---|---|---|
| Manufacturer's debug standard value | ＜14 | 4.5~6 | 2.5~11 | 5~8 | はい |
| (#1 コンプレッサー) before debug | 21.0 | 3.2 | -5.0 | 26.0 | いいえ |
| (#1 コンプレッサー) after debug | 12.3 | 5.0 | 5.8 | 7.6 | はい |
| (#2 コンプレッサー) before debug | 20.5 | 4.0 | 0.0 | 20.5 | いいえ |
| (#2 コンプレッサー) after debug | 13.9 | 5.2 | 6.0 | 7.9 | はい |
In this debug, the optimal overheat was 7.6℃ and 7.9℃ respectively.
| アイテム | Air conditioning air outlet | Air conditioning air outlet | Air conditioning air inlet | Air conditioning air inlet | Temp gap between air inlet and outlet |
|---|---|---|---|---|---|
| ユニット | 温度 (℃) | 湿度 (%) | 温度 (℃) | 湿度 (%) | (℃) |
| Before debug | 22.5 | 54.8 | 16.8 | 75.4 | 5.7 |
| After debug | 22.5 | 54.8 | 14.3 | 84.3 | 8.2 |
