Random 737 questions
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OK, more details.
If you look closer on the EDP, you see 3 hydraulic lines connected to the pump.
The supply line from the reservoir, the pressure line to the system and ... the case drain.
There is a small flow through the pump housing for lubrication and cooling purpose.
These case drain flows even when there is no system demand/flow.
But the case drain goes not go back directly to the tank. It is routed via 2 heat exchanger (case drain to fuel) in the wing tanks.
Without fuel in the tanks the complete system is getting to hot.
If you look closer on the EDP, you see 3 hydraulic lines connected to the pump.
The supply line from the reservoir, the pressure line to the system and ... the case drain.
There is a small flow through the pump housing for lubrication and cooling purpose.
These case drain flows even when there is no system demand/flow.
But the case drain goes not go back directly to the tank. It is routed via 2 heat exchanger (case drain to fuel) in the wing tanks.
Without fuel in the tanks the complete system is getting to hot.
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Without fuel in the tanks the complete system is not getting hot as the engines are not running, Or are you saying w!ith less than 760KG. Do you know if the case drain fliter has a bypass to prevent overheat in case of blockage?
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Sorry for the misleading wording. 
I meant "less than 760kg of fuel in each" tank. Below this level the heat exchanger are not any more fully surrounded by fuel.
No, there is no bypass.
If the filter starts to produce more resistance due to contamination, you have a increase of the EDP pressure. This is caused by the way the EDP regulates the output pressure.
So, a increasing pressure above the normal range (approx. 2800 - 3200 PSI) could be an indication for a "dying" EDP.
I meant "less than 760kg of fuel in each" tank. Below this level the heat exchanger are not any more fully surrounded by fuel.
Originally Posted by Avenger
...Do you know if the case drain fliter has a bypass to prevent overheat in case of blockage?...
If the filter starts to produce more resistance due to contamination, you have a increase of the EDP pressure. This is caused by the way the EDP regulates the output pressure.
So, a increasing pressure above the normal range (approx. 2800 - 3200 PSI) could be an indication for a "dying" EDP.
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Assumed Temp
Imbracablecrunk , there isnt any minimum percentage specified as to assumed being more than actual . You can feed anything higher than actual , the FMC will take it but may actually not reduce any thrust beyond the flat rating of the engine . You are gauranteed to get performance of 30c even with a assumed lesser than that and yes it is possible to feed assumed lesser than 30c , although it may not be of any real use . The only restriction that we use in our company is , not to do an assumed temp method if the difference between the ATOW and the limit weight is less than 500 kgs .
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I guess it depends on FMC version. We have quite a few planes that do not allow the pilot to enter any assumed temperature of 30 degrees or lower. I haven't flown enough recently to check if is something about 10.8A or some customization issue.
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Hi,
point 5) - The Bias factor on FMC is meant to cater for over all degradation. its a fuel milage offsetting factor. So it caters for engine as well as airframe(and other factors like wt etc).
point 6) I am not sure if the FMC will accept it or not, but thrust will be of the flat rate, and such assumed temp will have no benefit (of thrust reduction)
Hope it helps.
point 5) - The Bias factor on FMC is meant to cater for over all degradation. its a fuel milage offsetting factor. So it caters for engine as well as airframe(and other factors like wt etc).
point 6) I am not sure if the FMC will accept it or not, but thrust will be of the flat rate, and such assumed temp will have no benefit (of thrust reduction)
Hope it helps.
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Random 737 questions
Bill Buffler: if you lose B sys hydraulics and flaps are extended after take off, the LEDs can be retracted with PTU pressure using the alternate flap system.
Hydraulic pumps;
The fluid from the entire system is cooled by the heat exchangers in the tanks....so there is your requirement for 760kg (to cover the heat exchangers).
The overheat for the EMDP´s is measuring the temperature of the EMDP casings. They will heat up much quicker than the EDP´s due to the reasons Ifixplanes has said.
If you are tooling around with 700kg a side the fluid temperature will most likely rise. If you turn your EMDP´s off.....it will not rise as much.
Thats my take, happy to be corrected.
The fluid from the entire system is cooled by the heat exchangers in the tanks....so there is your requirement for 760kg (to cover the heat exchangers).
The overheat for the EMDP´s is measuring the temperature of the EMDP casings. They will heat up much quicker than the EDP´s due to the reasons Ifixplanes has said.
If you are tooling around with 700kg a side the fluid temperature will most likely rise. If you turn your EMDP´s off.....it will not rise as much.
Thats my take, happy to be corrected.
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LED's on ALTN:
IMHO if HYD B is not available, once the LED's are out they stay out. If HYD B is available LED's can be retracted, but the ALTN Flap switch has to be closed. So if you extended the TE flaps & LED's using ALTN Flap switch, and then wish to retract them with HYD B, first close the switch.
IMHO if HYD B is not available, once the LED's are out they stay out. If HYD B is available LED's can be retracted, but the ALTN Flap switch has to be closed. So if you extended the TE flaps & LED's using ALTN Flap switch, and then wish to retract them with HYD B, first close the switch.
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In the end, there must be a decent amount of heat generated by the mechanical A pumps because there is a heat exchanger in one of the fuel tanks for cooling . And the book says that you will get an overheat if the associated fuel quantity is too low, yet there is no overheat warning for the A system.
But perhaps this is an unusual enough situation that it didn't warrant overheat lights. Why? If your fuel is that low, your engines(and therefore the mechanically driven A pumps) will be shutting down soon enough anyways unlike the B pumps which could be left on all day with the fuel quantity low, perhaps by maintenance or pilots after landing with not much fuel.
Both A and B pumps appear to have the third port for case drain.
But perhaps this is an unusual enough situation that it didn't warrant overheat lights. Why? If your fuel is that low, your engines(and therefore the mechanically driven A pumps) will be shutting down soon enough anyways unlike the B pumps which could be left on all day with the fuel quantity low, perhaps by maintenance or pilots after landing with not much fuel.
Both A and B pumps appear to have the third port for case drain.
Last edited by JammedStab; 2nd Nov 2012 at 15:13.
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... Both A and B pumps appear to have the third port for case drain. ...
Already mentioned here.
... yet there is no overheat warning for the A system ...
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If you look closer on the EDP, you see 3 hydraulic lines connected to the pump.
The supply line from the reservoir, the pressure line to the system and ... the case drain. There is a small flow through the pump housing for lubrication and cooling purpose. These case drain flows even when there is no system demand/flow. But the case drain goes not go back directly to the tank. It is routed via 2 heat exchanger (case drain to fuel) in the wing tanks.
Without fuel in the tanks the complete system is getting to hot. "
I am pointing out that the electric pumps have the same thing(case drain). And why would I use the B pump overheat(EMDP as you call it) to tell if I have an overheat for the A Pump fluid.
Last edited by JammedStab; 2nd Nov 2012 at 17:49.
JammedStab, it sounds like you are confused about which pumps provide pressure for which system.
System A has an EDP and an EMDP.
System B has an EDP and an EMDP.
Please excuse me if you have that sorted and I have misinterpreted your posts.
System A has an EDP and an EMDP.
System B has an EDP and an EMDP.
Please excuse me if you have that sorted and I have misinterpreted your posts.
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I was only on the aircraft type for about 7 months and that was 2 years ago....
That being said, the thread has a generic title for 737. I flew the 737-200 series. I believe that my earlier statement is correct but welcome any corrections if you feel I am wrong that A-system is two engine driven hydraulic pumps, while B system is two electric pumps. No overheat indication for A system pumps. Both types have case drain fluid cooling, both systems have heat exchanger cooling in the fuel tanks and my previous statement was correct.
Can anyone confirm.
Later model 737's. Don't know a thing about them.
That being said, the thread has a generic title for 737. I flew the 737-200 series. I believe that my earlier statement is correct but welcome any corrections if you feel I am wrong that A-system is two engine driven hydraulic pumps, while B system is two electric pumps. No overheat indication for A system pumps. Both types have case drain fluid cooling, both systems have heat exchanger cooling in the fuel tanks and my previous statement was correct.
Can anyone confirm.
Later model 737's. Don't know a thing about them.
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If you turn the EDP off (not pull the fire handle), the pump operates in a "depressurized mode". In this mode, would you expect that the pump is not working as hard, so perhaps would run cooler?
According to the Maintenance Manual, even with zero fluid output from the pump (to airplane systems), the pump can still generate a fluid pressure of 2900psi (compared to 3030psi at 3750rpm at 37.5gallons/min in pressurised mode). Whether this slight reduction in pressure indicates a % decrease in work, I can't say.