DOC AIRBUS | AMM A320FTRANSIENT BLEED VALVE SYSTEM - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
1. General
(Ref. Table 001)
The Transient Bleed Valve (TBV) controls the flow of air from the 9th stage of the High Pressure Compressor (HPC) to the cavity in the Low Pressure Turbine (LPT).
This flow of air increases the compressor stall margin during engine transient conditions. The TBV is a two-position butterfly valve that is normally closed. It has one actuator and a valve body with one flow path. The TBV has a dual linear variable differential transducer (LVDT) that tells the Electronic Control Unit (ECU) the position of the valve.
** ON A/C NOT FOR ALL (Ref. Table 001)
Transient Bleed ValveThe Transient Bleed Valve (TBV) controls the flow of air from the 9th stage of the High Pressure Compressor (HPC) to the cavity in the Low Pressure Turbine (LPT).
This flow of air increases the compressor stall margin during engine transient conditions. The TBV is a two-position butterfly valve that is normally closed. It has one actuator and a valve body with one flow path. The TBV has a dual linear variable differential transducer (LVDT) that tells the Electronic Control Unit (ECU) the position of the valve.
2. Description
The ECU uses hydraulic fuel pressure from the Hydromechanical Unit (HMU) to control the position of the TBV. The fuel pressures used by the HMU are Pb, Pcr, and Pc. All three pressures come from the main fuel pumps, thus these pressures increase and decrease with the speed of the engine. Pressure Pb is the pressure of the boost stage discharge. The HMU controls Pcr to be 150 plus-or-minus 10 psig (1034 plus-or-minus 69kPa gage) more than Pb. The HMU controls Pc to be 300 plus-or-minus 10 psig (2068 plus-or-minus 69 kPa gage) more than Pb. The HMU applies pressure Pcr to the head end of the valve actuator. The HMU servo valve uses pressures Pb and Pc to send a control pressure Ptb to the rod end of the actuator.
In order to open the butterfly valve, the Ptb signal is changed from Pc to Pb pressure. The Pcr pressure overcomes the Pb pressure and the valve opens to increase the stall margin. The valve is held closed in normal operation by changing the Ptb signal from Pb to Pc pressure. The Pc pressure overcomes the Pcr pressure and the valve closes.
The ECU uses hydraulic fuel pressure from the Hydromechanical Unit (HMU) to control the position of the TBV. The fuel pressures used by the HMU are Pb, Pcr, and Pc. All three pressures come from the main fuel pumps, thus these pressures increase and decrease with the speed of the engine. Pressure Pb is the pressure of the boost stage discharge. The HMU controls Pcr to be 150 plus-or-minus 10 psig (1034 plus-or-minus 69kPa gage) more than Pb. The HMU controls Pc to be 300 plus-or-minus 10 psig (2068 plus-or-minus 69 kPa gage) more than Pb. The HMU applies pressure Pcr to the head end of the valve actuator. The HMU servo valve uses pressures Pb and Pc to send a control pressure Ptb to the rod end of the actuator.
In order to open the butterfly valve, the Ptb signal is changed from Pc to Pb pressure. The Pcr pressure overcomes the Pb pressure and the valve opens to increase the stall margin. The valve is held closed in normal operation by changing the Ptb signal from Pb to Pc pressure. The Pc pressure overcomes the Pcr pressure and the valve closes.
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| ! Actuator Stroke ! Mode ! TBV Position ! |
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| ! 0% ! No Air ! Closed ! |
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| ! 100% ! Transient Bleed Air ! Open ! |
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| TBV Operation |
| Table 001 |