Corsair2
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Cessna 172S Fuel Selector Valve

Sat Mar 05, 2005 12:29 am

Under what circumstances would I want to put the fuel selector valve in the left or right position rather than using both tanks?
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2H4
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RE: Cessna 172S Fuel Selector Valve

Sat Mar 05, 2005 12:44 am

This is from the 172R Information Manual, but it applies to the S model as well:


Operation from either LEFT or RIGHT tank is reserved for cruising flight.

When this fuel selector valve handle is in the BOTH position in cruising flight, unequal fuel flow from each tank may occur if the wings are not maintained exactly level. Resulting wing heaviness can be alleviated gradually by turning the selector valve handle to the tank in the "heavy" wing. It is not practical to measure the time required to consume all of the fuel in one tank, and, after switching to the opposite tank, expect an equal duration from the remaining fuel. The airspace in both fuel tanks is interconnected by a vent line and, therefore, some sloshing of fuel between tanks can be expected when the tanks are nearly full and the wings are not level.



Hope that helps you out.


2H4


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SATL382G
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RE: Cessna 172S Fuel Selector Valve

Sat Mar 05, 2005 12:54 am

Isn't it common practice to safety wire this valve to both?
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corey07850
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RE: Cessna 172S Fuel Selector Valve

Sat Mar 05, 2005 2:16 am

Quoting SATL382G (reply 2):
Isn't it common practice to safety wire this valve to both?


I've never seen it...
 
Alias1024
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RE: Cessna 172S Fuel Selector Valve

Sat Mar 05, 2005 2:34 am

As said by 2H4, unequal fuel flow is the most common reason.

Another reason would be if you developed some sort of fuel leak out one wing. You wouldn't want the tank to run dry when you are still drawing fuel from it. Air would then be drawn into the fuel lines, and that would ruin you day.
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777wt
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RE: Cessna 172S Fuel Selector Valve

Sat Mar 05, 2005 3:44 am

During shutdown and securing the aircraft, the fuel selector must be set to left or right. I think the same applies for refueling the aircraft too.
 
Fly2HMO
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RE: Cessna 172S Fuel Selector Valve

Sat Mar 05, 2005 5:24 am

Embry-Riddle standard operations are to set the fuel selector to either side when parked. This prevents fuel moving from one tank to the other if the ramp is not level, which certainly applies to our ramp  yes 

Occasionally the fueling guy won't pay attention to what he is doing and fill the tanks unevenly. This will make the plane bank to the side, which is very annoying. Thus, you put the fuel selector to the heavy tank and burn the extra fuel until the tanks are equal.

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777wt
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RE: Cessna 172S Fuel Selector Valve

Sat Mar 05, 2005 7:44 am

Also if your a newbie and doing alot of traffic pattern and touch n' go's or turns around a point, the higher wing will be used up most of the time.
 
57AZ
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RE: Cessna 172S Fuel Selector Valve

Mon Mar 07, 2005 6:12 am

The requirement for the fuel selector to be set to L or R at shutdown is only for the R and S models I believe. Older 172s can be shut down and secured with the selector set for Both. However, the selector must be set for Both during takeoff and landing operations. Crossfeed valve are more commony used on multi-engine aircraft. We hardly use the crossfeed valve on our 172/R whereas on the 414 it's not uncommon to use it. Reason being that on the 414, the normal procedure is to feed each engine from the tanks on that side. However, slight differences in power setting can create an imbalance. To correct the imbalance the crew can take one of two actions: increase the power setting on the heavier side or crossfeed. On the 400 series twins, there are two individual crossfeed valves. One is the No. 1 engine and the other is No. 2. Crossfeed shutoff (emergency or otherwise) is handled by the Emergency Crossfeed Shutoff valve, located between the No. 1 and No. 2 fuel selectors. Due to the fuel system design on the 400 series, the only way to prevent fuel from moving from the high tank to the low tank on an uneven ramp is to actuate the Emergency Crossfeed Shutoff valve. On our plane, normal practice is to leave this valve in the closed position except during flight operations.
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bri2k1
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RE: Cessna 172S Fuel Selector Valve

Mon Mar 07, 2005 12:02 pm

The N and Q models I fly specify to put the fuel selector to one side only during parking, and only when on an uneven surface. It is not prohibited to move it to one side or the other for other flight regimes, but checklists predicate both for engine start, run-up, descent, and landing.
Position and hold
 
liamksa
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RE: Cessna 172S Fuel Selector Valve

Mon Mar 07, 2005 6:34 pm

We hardly use the crossfeed valve on our 172/R whereas on the 414 it's not uncommon to use it.

Crossfeed on a 172R?  eyebrow  You probably don't use it much 'caus it doesn't exist 57AZ  cheeky . Crossfeed usually refers to the ability to feed the right engine with fuel from the left tank (anb vice versa) for extended flights with 1/INOP.

Trivia: Why to most 172s tend to take more fuel from the left than right tank initially?
 
N766UA
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RE: Cessna 172S Fuel Selector Valve

Mon Mar 07, 2005 8:56 pm

It's good practice when you're trying to conserve fuel to switch back and forth regularly over a long flight. Every half hour or so usually does the trick. Also, when fueling the aircraft one should switch to just one tank to prevent any cross feeding to get the maximum amount of fuel possible in the tanks.
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727EMflyer
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RE: Cessna 172S Fuel Selector Valve

Thu Mar 10, 2005 9:47 am

It would be a very bad idea to wire the valve in "both." In an emergency situation you need the ability to select "off" for fire prevention.
 
2H4
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RE: Cessna 172S Fuel Selector Valve

Thu Mar 10, 2005 1:58 pm



Quoting Liamksa (Reply 10):
Trivia: Why to most 172s tend to take more fuel from the left than right tank initially?

....Because that's the side the fuel vent is on?


2H4


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bri2k1
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RE: Cessna 172S Fuel Selector Valve

Fri Mar 11, 2005 11:49 am

My guess is it has something to do with P-factor?
Position and hold

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