Don, You are correct. The cups used for DOT brake fluid is made of EPDM (ethelyene propelyene -this might be misspelled) rubber. The rubber used for regular oil base hydraulic fluid is acrylonitrile bunadiene, commonly called buna or nitrile rubber. This is by far, the most common rubber used in hydraulic systems like you find in earth moving equipment - Caterpillar, Case, John Deere, etc.
These cups are readily available and are made of buna rubber which is the rubber of choice for oil base hydraulic fluid, which includes the 5606 approved for aviation use. Now the problem is that technically we can't go to a hydraulic seal distributor and buy these cups and put them in an airplane. Am I right about this? Somebody in the group who is knowledgeable about all the red tape can tell us. If I'm wrong about this and we can legally put buna cups in our airplanes, purchased from industrial suppliers, let me know. I've worked in the fluid power industry for 30 years and I know where to get them. Here's my soap box... Yes, we can buy parts to put into mobile cranes that lift thousands of pounds hundreds of feet into the air and put hundreds of people at risk but you can't put that same part in a two seat airplane. Ok, I'm off my soap box now. The good news is that the world has a cup that can be used in hydraulic oil and is readily available. Darick ----- Original Message ----- From: "Donald" <[email protected]> To: [email protected] Sent: Friday, May 28, 2010 3:24:03 PM GMT -05:00 US/Canada Eastern Subject: [ercoupe-tech] Re: Filling the MLG struts What the world really needs is a cup that can be used in hydraulic oil! I wonder what happens when one puts hydraulic oil into the strut that has been converted to the rubber cup? Many industrial applications use those same type cups in hydraulic oil, made of a different compound I suppose. --- In [email protected] , William R. Bayne <ercog...@...> wrote: > > > There is more than a little possibility of confusion by the less > experienced in reading these two posts. > > I agree with Alan that the rubber cup is a better design (for proper > long term oleo seal service) than the O-ring installed in later birds. > The rubber cup was the earlier design, though. IMHO, the O-ring was > NOT an improvement; but if your oleos are not worn to the point that > the O-ring cannot seal properly, or needs replacement often, install > the Skyport "cup kit" SMK-61. It is the "better now" to which Alan > refers. Individual cups are available as Skyport part number SS12301. > > For anyone interested, the oleo snap ring (part number 415-33229-1, see > Fig. 12, item 18, NOT clearly shown and perhaps no longer available > from Univair or Skyport is/was a "Reliance Light External Ring for > 1.250 shaft, .125 x .620 wire section, .250 gap, style #6 gap" from > Eaton Mfg. Co., Massilon, OH. > > Donald is correct that DOT 3 brake fluid will destroy oleo O-rings > (just as hydraulic oil will destrot rubber cups). That should come as > no surprise, as this the lubrication instructions are specific. Many > mechanics don't know about the Skyport kit, and blindly service oleos > according to ERCO's serial number recommendations (thus assuring > failure of installed rubber cups on later birds). If rubber cups are > installed, brake fluid MUST be used as oleo fluid. It may be that DOT > 5 (silicone) brake fluid will not destroy AN O-rings...I have not > tested that. > > The "old time spring cap" (and tube) deteoriate. Due to rusting, many > no longer have spring closure action. Replacements are available from > Skyport (and perhaps Univair). Forney used Gits Bros. #402, Style "E", > but there may be other sources of such a generic item. Some mechanics, > not knowing that replacements are available may have tapped the oleo > hole to receive the pipe plug Alan describes. > > The pipe plug was "production" on Ercoupes through serial 812 (per > Parts Catalog Fig. 11, p. 12, (upper) item 14. If this item were > correctly referred on facing page 13, I believe it is the final item > listed under 12a as "AN913-1D, Plug - hex (415-33166-3). > > Due to the many production changes to Ercoupe design and service parts, > it is important that posters identify the serial number of the aircraft > their experience (and information) relates to. A list of many of such > changes in inside the back of the Service Manual. "One size DOES NOT > "fit all" in this context, and no one intends to mislead or wants to be > mislead. > > Regards, > > William R. Bayne > .____|-(o)-|____. > (Copyright 2010) > > -- > > On May 27, 2010, at 12:17, Donald wrote: > > > > > > > You speak of a filler plug with safety wire. My two sets of struts > > have an old time spring cap like was used on oil holes a long time > > ago, must be a change along somewhere. > > I opted to use only new O rings, and the red aviation hydraulic fluid, > > nice and oily. After seeing what brake fluid did to my other set, no > > brake fluid for me. > > > > .--- In [email protected] , ALAN FAIRCLOUGH > > <texasaviator@> wrote: > >> > >> How to and what not to do... > >> > >> I have found there are several things to watch out for. > >> > >> > >> First of all, jack up the plane so the weel extends all the way down. > >> Push the wheel up and down to feel the current hydraulic damping. > >> > >> If it is good, your sysyem is working and may just need topping off. > >> If it is not you will feel it when pushing the wheel up. > >> > >> First thing to check is the bumpers. these are little rubber stops on > >> the landing gear leg and on the strut. When the wheel drops down, the > >> motion is stopped by a rubber bumper that is attached to this little > >> arm. If it is missing, which is quite common, you are in trouble. > >> The wheel has been dropping too far down, the filler hole has a rough > >> edge on the inside of the > >> cylinder and it destroys the seal. if you have a seal cup version. If > >> you have the O'ring version, you need to take it off and get a seal > >> cup kit from Skyport. > >> The O'ring version was made to last 10 years at best and none will > >> last long. It was a great idea at the time but there is better now. > >> > >> When you take the cylinder apart, you will see if you have the cup or > >> the O'ring. You can leave the O'ring on as it will not harm anything. > >> You will have to wash out the cylinder which is made of steel and > >> probably has rust on the inside. Go to the auto parts store and buy a > >> small 3 blade fine ctlinder hone that will fit inside. ( take the > >> cylinder with you to test if it fits or make a second trip). You then > >> hone out the inside surface with this device in a power drill and > >> with diesel or kerosene in the cylinder. If you don't do this, the > >> rust will eat up your cup seal. > >> Wash it out well. Clean up the piston surface with sandpaper and > >> diesel or with a wire wheel brush and install the cup kit as > >> instructed. > >> I find it is easier to fill the cylinder before installing it on the > >> plane. Just pour the fluid into the cylinder and inser the piston > >> seal and slowly push it down. Any excess fluid will come out the fill > >> hole. inser the plug into the fill hole and safety wire. > >> Put it on the plane and test the damping motion. > >> > >> If you need to top off the fluid, remove the rubber bumper and > >> inspect it. Drop the wheel as low as it will go and add fluid through > >> the filler hole. I use that syringe the dentist gave me to irrigate > >> my wisdom tooth hole. An old oil can also works. > >> The U cup seal is now above the filler hole. Do not push the wheel up > >> now. > >> Fill with fluid until it runs over and then push a wooden chopstick > >> into the hole to carefully help the cup lip over the filler hole > >> inside surface while slowly pushing the wheel up. Once the U cup seal > >> is below the filler hole, prop the wheel up so it does not drop again > >> and re-install the filler plug with safety wire and re-install rubber > >> bumper. > >> > >> With the rubber bumper installed, you can now drop the wheel all the > >> way down again and the U cup seal will remain below the filler hole. > >> Now test the damping. > >> > > > > > > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > > > > >
