Gascolator or not?

float208 · #1 03-26-2009, 08:04 AM

How many people use a Gascolator with an injected engine and AFP fule pump? Pros vs. Cons anyone?

Thanks.

AltonD · #2 03-26-2009, 08:13 AM

I didn't install one (and I have not flown yet). Van's does not reccomend one with the AFP pump and fuel injection.
but, if you wanted one, go ahead. The down side is more exposed, uninsulated fuel system componenets under the cowl: more prone to vapor lock.

N55CU · #3 03-26-2009, 08:27 AM

I didn't put one in with the IO-360 and AFP pump / no issues after 190 hrs
Randy Utsey
RV-7 / Charlotte, N.C.

beechrv9a · #4 03-26-2009, 09:03 AM

Quote:

Originally Posted by float208

How many people use a Gascolator with an injected engine and AFP fule pump? Pros vs. Cons anyone?

Thanks.

I just got off the phone with Airflow Performance with this same question. They did not recommend installing one. His comment with fuel injection was that any water in the line at this point with just get pushed out throught the injectors. And besides, there are drains in each wing.

Norman CYYJ · #5 03-26-2009, 10:06 AM

In Canada the plane must have a gasculator no way around it. If the plane is to be sold into Canada one will have to be added.

JoeBlank · #6 03-26-2009, 10:25 AM

and AFP pump, filter, and servo on my RV-6... I originally installed a GAS-3 in the left wing root, but have never found much of any water or debris in it. Downstream at the AFP filter, it has always been very clean upon annual inspections. IMHO the gascolator is overkill on this type of system. Since the wing drains are the lowest point in the system, it would require a LOT of water there to make it's way up into the rest of the fuel system. TT in service, ~580 hours with no problems...

vlittle · #7 03-26-2009, 11:44 AM

I just installed an Andair Gascolator upstream of my AFP fuel pump for the Rocket. The Gascolator is about the same price as an inline fuel filter, but is easier to service.

Since it's a Canadian requirement, the decision was easy. I drilled a hole in the bottom skin for a quick drain valve. It's not just water that is trapped by the gascolator. Sometimes I get small particles as well, and it's a good heads up to check the rest of the fuel system.

Vern

roee · #8 03-26-2009, 01:53 PM

A while back I posed the same question to Don Rivera at Airflow Performance. He sent me the following write-up:

Quote:

To fully understand the situation you must first understand why a gascolator was used in the first place. Back when carburetors were the only source of fuel metering on aircraft, water was a detriment to the operation of the engine. Of course water won?t burn but the main reason was that water being heaver than fuel would sink to the bottom of the float bowl. Water also has a higher surface tension than fuel. Since the main jets are located in the bottom of the float bowl and the metering head (the suction created by the venturi to suck the fuel out of the bowl) is low on a carburetor, the water can actually block the flow of fuel through the main jets due to surface tension, thus starving the engine of fuel.

Enter the fuel injection system. There?s no float bowl, the fuel is under pressure (20-30 PSI). So in this case even if there?s some water in the system the fuel control will flow the liquid what ever it is. Granted the engine cannot burn water but there will be no interruption of the delivery of fuel to the engine.

One thing that is in the carburetors favor is that with the float bowl, if any foamy fuel or fuel vapor is in the system, the float bowl will vent off the vapor and the main jets are only exposed to liquid fuel. Correct fuel metering in this case is mostly not effected. Unless the engine driven fuel pump or boost pump is vapor locked the engine will get fuel. In this respect, carburetors are less affected by hot operation. More on that subject later.

Now look at the aircraft fuel system. In an RV aircraft the fuel tanks are the lowest point in the fuel system. Water will be in the sumps of the tanks. If water is found during a sumping operation then further investigation should be made concerning the entire aircraft fuel system condition.

1.Installing a gascolator in any other place other than the wing roots would result in the gascolator being higher than the lowest point in the fuel system. Not the place to catch water.

2.Since the RV aircraft can do some aerobatic maneuvers, rolling the aircraft upside down would dump any water into the fuel system if any were held in the gascolator.

3.Since the fuel injection system does not have a float bowl, fuel vapor is a problem and can cause poor fuel metering. Avgas boils at around 130 degrees F at sea level. The boiling point gets lower as altitude increases and also with a decrease in fuel pressure on the suction side of the fuel pump (flow losses in the fuel system). Since the gascolator is typically installed on the firewall, it is subject to a high heat environment. The volume of fuel in the gascolator does not change very fast at low power therefore the fuel in the gascolator picks up heat, which can lead to fuel vapor issues and possible vapor lock of the engine driven fuel pump.

4.Installation of the gascolator on the fire wall though not recommended on this installation can be accomplished by the following:
a.Make sure the gascolator can withstand 30 PSI, as it will be pressurized when the boost pump is on.

b.Install a blast shield over the gascolator and provide blast air to keep the gascolator cool.

c.Understand that having a volume of fuel on the firewall (gascolator) may result in rough engine operation and poor idle, under hot conditions.

d.With fuel injected installations we want to minimize the volume of fuel in the engine compartment as much as possible. This applies to hose routing and components that increase the volume of fuel that can be heated.

vlittle · #9 03-26-2009, 02:29 PM

In my installation, the Gascolator is there to meet the Canadian requirements, not necessarily to trap water. There is no way around this because fuel system problems have historically been the leading cause of failure in homebuilts. Hence, the mandatory inspections in Canada require the gascolator.

Using the Andair unit, it has a replaceable filter, thus serving the purpose to have a filter on the inlet of the AFP fuel pump, for about the same cost. With all due respect to AFP, not all aircraft are built and certified in the USA.

frazitl · #10 03-26-2009, 07:08 PM

I had the same question about 2 yrs ago and decided to replace the afp filter with an andair gascopator. I wanted the gascolator at the lowest point and on the cool side of the firewall. Took some careful tube bending but it is mounted in basically the same spot as the afp filter. I also didn't want to suck feul thru two filters agravating any fuel vapor problems. Not flying yet - probably next month. YMMV