aerotech777
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Vacuum Waste Vs Recirculating

Sun May 19, 2013 9:07 pm

Hi,

Modern aircraft are fitted vacuum waste system at the opposite of old aircraft that are fitted with recirculating waste system.

a) What are advantages and the disadvantages of vacuum waste system?

b) What are advantages and the disadvantages of recirculating waste system?

c) How often the toilet is used in short/medium aircraft? How full the waste tank?

d) Do you think it is worth to use recirculating waste system in modern short/medium aircraft? If yes/no, why?

Feedback appreciated.
 
rrobards2
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RE: Vacuum Waste Vs Recirculating

Mon May 20, 2013 12:15 am

The vacuum system is lighter. You're not carrying around blue water, only liquids in the vacuum storage tank is the waste itself and the little bit of water used during the flush.
Not to mention that blue water becomes VERY smelly after a while of use.

As far on short/medium haul aircraft, it's still better for the vacuum system. On our 737s, at MOST, the waste tank will fill up half way on a 5-6 hr transcon flight...and that's if people are constantly using it.

The only pro thing I can think of for the blue water system is the simplicity of it.
 
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1337Delta764
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RE: Vacuum Waste Vs Recirculating

Mon May 20, 2013 1:25 am

Quoting rrobards2 (Reply 1):
As far on short/medium haul aircraft, it's still better for the vacuum system. On our 737s, at MOST, the waste tank will fill up half way on a 5-6 hr transcon flight...and that's if people are constantly using it.

Interestingly, Boeing chose to use a vacuum flush system on the 767 but for some unknown reason chose to use the recirculating blue liquid on the 757 (at least until the release of the 753, which has the vacuum flush system). Meanwhile, Airbus used to give airlines the choice of either system on the A300, A310, and older A320 aircraft.
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SXDFC
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RE: Vacuum Waste Vs Recirculating

Mon May 20, 2013 5:14 am

From a ground crew's point of view, with the vacuum system there is only one service port, with the traditional circulation system there are more than one ( I've only worked on the 737 ) and I know that the -300s and -500s have two lav service ports and the -700s and -800s have only one. Also when servicing a -300 or -500 in the winter time and the fill port is frozen, you have to "top fill" ( poring blue juice into the toilet itself ).
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737tdi
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RE: Vacuum Waste Vs Recirculating

Mon May 20, 2013 4:05 pm

The biggest advantage of the vacuum over blue water is secondary cost. By this I mean the amount of damage that occurs to an aircraft using recirculating lavs. I.E. Blue water spills, they happen on a fairly regular basis when dealing with 500+ aircraft. If it is the fwd. lav. the spills and leaks happen just above all of the E&E racks on the 737, this can be quite a nightmare to clean up and repair. 2nd. is the amount of corrosion that these spills can cause, a corroded lav. wall post repair can take an aircraft out of service for a couple of days.

All hail the vacuum system, it is a great advancement due to reliability, maintainability, cleanliness and above all, not near as smelly.
 
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1337Delta764
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RE: Vacuum Waste Vs Recirculating

Mon May 20, 2013 8:29 pm

So, does anyone know the particular reason Boeing chose to go with the vacuum flush system on the 767 while chose to use the recirculating liquid on the 757?
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SXDFC
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RE: Vacuum Waste Vs Recirculating

Tue May 21, 2013 6:08 am

Quoting 1337Delta764 (Reply 5):
So, does anyone know the particular reason Boeing chose to go with the vacuum flush system on the 767 while chose to use the recirculating liquid on the 757?

I am no MX expert but from what I remember the vacuum flush was first introduced on the 763, since the 752 and 762 were introduced around the same time, they shared the same recirculating flush system. I've also heard that some of the 757s have about 4 service ports because of this. Please don't quote me as I am pretty sure I've read this on here, and I have never worked either A/C type.
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1337Delta764
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RE: Vacuum Waste Vs Recirculating

Tue May 21, 2013 3:10 pm

Quoting SXDFC (Reply 6):
since the 752 and 762 were introduced around the same time, they shared the same recirculating flush system

Nope, the 762 also has the vacuum flush system. I remember flying one in the summer of 1996 on DL (on ATL-SJU), and it the loud noise scared the heck out of me.
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planenut767
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RE: Vacuum Waste Vs Recirculating

Tue May 21, 2013 3:54 pm

Probably the biggest disadvantage to a vacuum waste system is that when you have a clog in the system, it usually takes out multiple lavatories, where as on a recirc water system it's normally just the one. Clearing them out is pure hell (especially in the summer months), but then again anything involving toilets, regardless of the system type usually is. For me personally I think they need to come up with a better designs for the vacuum waste systems.
 
SXDFC
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RE: Vacuum Waste Vs Recirculating

Tue May 21, 2013 7:08 pm

Does anyone know what type of lavatory system the old prop liners used to use? ( Constellation, DC-4/6/7, Electra, etc )
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Tristarsteve
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RE: Vacuum Waste Vs Recirculating

Tue May 21, 2013 7:19 pm

When vacuum flush systems were first introduced around 1983 they were very unreliable. Blockages were common. On the basic B757 with toilets at front and rear it was not worth the trouble, but the B767 with toilets spread across the aircraft, and more of them, it was.
When the A320 was introduced 4 years later, Airbus gave the buyers the choice. As far as I know only BCal opted for the blue water lavs, and in BA we suffered from this decision for the next 20 years. The A320 blue water lav was very unreliable, and the vacuum system was much better. Another problem was that because these 10 aircraft were the only A320 with a fwd toilet service point, most ramp workers managed to forget it, so the toilet filled up on the next sector.
What brought the vacuum system into universal use was very regular maintenance. The flush pipes are cleaned properly every week, but it is worth it.
 
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1337Delta764
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RE: Vacuum Waste Vs Recirculating

Tue May 21, 2013 7:48 pm

Quoting Tristarsteve (Reply 10):
When the A320 was introduced 4 years later, Airbus gave the buyers the choice. As far as I know only BCal opted for the blue water lavs, and in BA we suffered from this decision for the next 20 years. The A320 blue water lav was very unreliable, and the vacuum system was much better. Another problem was that because these 10 aircraft were the only A320 with a fwd toilet service point, most ramp workers managed to forget it, so the toilet filled up on the next sector.

FYI, AA's A300s had the vacuum flush system. I presume it later became an option on the A300 and A310 as well.

For McD aircraft, the MD-11, MD-90, and 717 (MD-95) have the vacuum flush system.

[Edited 2013-05-21 12:56:25]
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Skydrol
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RE: Vacuum Waste Vs Recirculating

Wed May 22, 2013 2:19 am

Quoting aerotech777 (Thread starter):
Modern aircraft are fitted vacuum waste system at the opposite of old aircraft that are fitted with recirculating waste system.

a) What are advantages and the disadvantages of vacuum waste system?

b) What are advantages and the disadvantages of recirculating waste system?

c) How often the toilet is used in short/medium aircraft? How full the waste tank?

d) Do you think it is worth to use recirculating waste system in modern short/medium aircraft? If yes/no, why?

Vacuum System advantages:

- lighter, single holding tank, less pre-charge weight
- better flexibility for lavatory positions within the cabin
- single point ground servicing (usually)
- reduced odors for passengers seated near the lavatories, cabin air is drawn overboard when the toilet is flushed
- no space required within the lavatories for holding tanks
- ''free'' vacuum energy source using differential pressure at cruise altitude


Vacuum system disadvantages:

- loud flush, if you are sitting within five rows of the lavatories in an airplane equipped with vacuum toilets, the almost endlessly-repeating flush suction noise gets tiring after a few hours.
- vacuum waste lines in the cabin floor/cargo area ceiling are a filthy nightmare to service when they get blocked
- toilet bowls are dry, and flush with only a few ounces of water, all of which gets sucked out... even with Teflon-coated toilet bowls, ''shit sticks''; it can get ugly for subsequent passengers
- as powerful as the flush is, the narrow-diameter lines get blocked easily by passengers flushing trash
- a failure in the vacuum system disables several (or all) toilets, depending on system size and redundancy
- loss of potable water results in very poor flush, clogs and inop toilets
- requires an electrically-operated vacuum pump for toilet flush at altitudes below 16,000 feet, and when the airplane is on the ground


Recirculating System advantages:

- much, much quieter flush than vacuum system
- simpler system to maintain
- toilets bowls are flushed very well by a pump, and stay cleaner than vacuum toilet bowls
- does not consume potable water
- essentially a porta-potty, toilets cannot become inop, even if they cannot flush
- if it can fit through the bowl trap, it will flush. (only to become a problem later when trying to empty the holding tank - diapers, bottles, towels etc.)


Recirculating System disadvantages:

- multiple ground service points
- more potential for leaks leading to corrosion in adjacent areas
- color of flush fluid evolves from bright blue to dull green to brown through the duration of a long flight
- odor of above described fluid also evolves accordingly


C - Judging by line-ups, lots.


D - Yes. If there is only one toilet, I believe the recirculating system would be used, since vacuum system just adds complexity, with little benefit, since one holding tank would by required either way.


Note: Lockheed 1011 recirculating system was different, and five aft lavatories used a common holding tank in the aft cargo area, similar to a vacuum system


My .02 having worked on these systems, and using them as a passenger.




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1337Delta764
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RE: Vacuum Waste Vs Recirculating

Wed May 22, 2013 5:40 am

Quoting Skydrol (Reply 12):
Note: Lockheed 1011 recirculating system was different, and five aft lavatories used a common holding tank in the aft cargo area, similar to a vacuum system

I remember the five aft lavatories in the L-1011 in their unique circular arrangement:


Since the main galley on the L-1011 was below the main deck, Lockheed was able to use the aft space to cram five lavatories where a galley would normally be located otherwise.
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wn676
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RE: Vacuum Waste Vs Recirculating

Thu May 23, 2013 10:20 am

Quoting SXDFC (Reply 6):
I've also heard that some of the 757s have about 4 service ports because of this. Please don't quote me as I am pretty sure I've read this on here, and I have never worked either A/C type.

Four ports at three service points is the most I've seen. They're a real pain to service. On our 757s you have two ports just aft of the main gear bay for the 3L/3R lavs, one port underneath either the 2L or 2R door depending on the configuration, and one just aft of the nose gear for the FC lav. Takes about 15 minutes to do correctly IF the fill ports aren't frozen. If they are, then you have to top fill which means two trips per lav up the jetway stairs with a full bucket of blue juice.
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n901wa
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RE: Vacuum Waste Vs Recirculating

Thu May 23, 2013 3:14 pm

The L-1011 also had a system where, if you flushed 1 lav, it would turn on a pump that would send pressured Blue water to all the lavs in that area. The Flush Valve on the side of the bowl would open and send water to the bowl. I have seen a new amt try to change the flush valve without pulling the CB and a cleaner flush a lav in the same area. A Nice Blue Fountain  
The 767-200 I worked on all had Vac system. In fact ABX has a 767-200 that they modified to take a Recirc lav in the fwd pos and took out the Vac system, and the patch where the dump valve is located is huge.
If I remember right the Ex PAA A310 had a Recirc system. I remember the first night we got a PAA 310 the 2L lav was leaking and the carpet was soaked, and had a Blue wave that started at 2L and went across the outside of the fues. Like someone had painted it on the acft.
The Worst was the MD-11 Lav system. I remember that it had a override system that the crews knew about, and if they kept resetting it so it would flush, the tank would go pass full, and get sucked into the blower, and out the side of the acft. Changed a few Blowers due to that. Also for some reason, there was a elbow that was a little to sharp on the Left side in the back under the floor, that would get plugged easy. Cat tell you how many times we took it apart.
Overall it was a toss, the Vac sys has issues, Sensors, flush valves, timers. The Recirc sys has, dump cables, and pumps at all locations and will work until it overflows.
 
SXDFC
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RE: Vacuum Waste Vs Recirculating

Thu May 23, 2013 3:53 pm

Does anyone what type of system the old prop planes ( DC-4/6/7, Connie, Electra ) had? Was it a recirc system too?
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