The International Cessna^® 170 Association

gahorn wrote: The 2H3-12 has only two fittings, one an inlet, the other an outlet. They are one a 5/8" and the other a 3/8" fitting at an angle. You probably want the 2H3-6 with two 5/8" straight fittings. Although not being used on a vacuum pump and therefore not critical to prevent pump failure, the "garter" filters must nonetheless be changed annually to prevent damage to the regulator valve itself. They are cheap insurance.

gahorn wrote:
Re: Initiating flight with gyros not yet up to speed: It is highly desireable that aircraft equipped with venturis have cageable gyros. The old AN gyros were equipped with provisions for Caging knobs, but some have had them removed. This is an error in my opinion, and the caging knobs should be re-installed. The AN 5736 horizon specs call for 6 minutes of 3.5 inches vacuum to come up to the correct indication from an un-caged position. A gyro that is caged will start out at the straight/level indication and so is much faster to get into action. Similar behavior is applicable to the AN 5735 DG.
Newer-style gyros are only rarely cageable because they have different operating limits. While the AN 5736 horizon has gimbal limits of 60-degrees pitch and 90-degrees bank (as did the early pictorial styles), most newer pictorial gyros do not. What this means is that with AN gyros when the limits are exceeded (such as during aerobatics) the gyros will either "tumble" or precess to an unuseable indication, requiring re-setting them with the caging knob. (They will self-erect after about a 10-minute recovery. Hmmmn. That sounds familiar. )
Exceeding the limits on all gyros, both AN and pictorial, places excessive wear on the bearings. That is why AN's are equipped with and should be caged with their caging knobs before aerobatics (and why aerobatics should not be performed with non-aerobatic model pictorials.) The same is true of cageable gyros before and after fight. They should be caged until after takeoff, and should be caged after landing and arriving at the chocks. This applys to both 5736 horizons and 5735 DG's.

N3243A wrote:

gahorn wrote: The 2H3-12 has only two fittings, one an inlet, the other an outlet. They are one a 5/8" and the other a 3/8" fitting at an angle. You probably want the 2H3-6 with two 5/8" straight fittings. Although not being used on a vacuum pump and therefore not critical to prevent pump failure, the "garter" filters must nonetheless be changed annually to prevent damage to the regulator valve itself. They are cheap insurance.

George,

According to the Chief Aircraft on line catalog, the 2H3-12 has a 5/8" inlet and two 3/8" outlets, the second of which is at a 45 degree angle from the first. The picture in the link below, (while supposedly the Airborne model) is actually the Rapco copy of the Airborne model 2H3-12 (which for some reason does not have a PMA?). It clearly shows 2 outlets.
If I use the 2H3-6 per your recommedation, I will have one 5/8" outlet then I will have to have the 5/8" outlet hose going into a T-splitter then out with 2 3/8" hoses to the gyros. Splitting at the regulator itself or at a T-fitting, what's the difference? Are there variations in the spec of the relief valve itself?

http://www.chiefaircraft.com/Aircraft/V ... 2H3-12.jpg

gahorn wrote:Whenever in doubt about such things, it's a good idea to consult the Illustrated Parts Catalog for your aircraft.
The 170B IPC, pgs 130/131, Figure 77, item 13, pn 0511059 is likely a Garwin unit, which can be purchased from most salvage yards.