Boo boo boo. Troy Bilt is now an MTD product. Go tho their web site "mtdproducts.com" or the link below take you directly to the page you need. They have a long list of Horse models, left side has Horse model, right has engine model if you can't determine the unit number. Click on appropriate model, opens a new window, click on list showing group sections, the one starting with speed control or something like that will show the reverse disc. Find the part number and then order direct from MTD Here is a link that might be useful: MTD/TroyBilt

I would think that the weight is really due to water. If sediment is the problem, you should see sediment at other faucets too. You could cut open the first filter unit to see what's really trapped if you want to. Typically the pre filters need to be changed several times per year, depending on the usage. The main components are 1. Sediment pre filter 2. Carbon pre filter(s) 3. RO membrane filter 4. Storage tank 5. Carbon post filter The water comes in @ main line pressure. There is a pressure differential @ the RO membrane filter stage which discharges directly into the drain. Some possible problems would be 1. Sedimentation which would reduce the pressure differential. 2. Extremely hard water which clogs up the membrane filter. Symptom - continual discharge since less filtered water enters the storage tank. 3. Low pressure in the storage tank. Symptom - low output, storage tank remains heavy.

1. The three connection faucet the RO comes with is an air gap faucet and is code compliant in lots of locations. That design protects against cross-contamination as the RO drain line connects to the sink drain. 2. Some ROs do and most don't. 3. The final, or post filter, is a taste filter. If you like the way RO water tastes then you can eliminate that filter but the reason it's there is that many people don't like the taste of RO water. 4. The storage tank is pressurized to 6-7 lbs/in2 with NO water in the tank. It is a small volume and easy to damage the internal bladder so using a hand (bicycle) pump is safer than using a compressor. Other than flushing the internal bladder and sanitizing at service intervals there no maintenance the tank requires. Since you got this RO free on Craigslist you should make sure that... There is a proper size flow restrictor for the output of the membrane and a check valve. Also, there must be an automatic shut-off or the RO will continue to dump to drain after the storage tank is filled. Use PE (polyethylene) tubing and not copper to plumb the RO. John Guest (push-in) style connectors are a real time saver and make for a sano installation. Use a proper fitting to feed the RO and not a saddle (piercing) valve.

Your missing part is a FLOW RESTRICTOR and should be replaced when ever the membrane is replaced. It regulates the water flow to drain, not air. If the old one is still in there you can remove the old one and clean it carefully... it clogs with debris. The shut-off valve pictured above is exactly that... a shut-off valve. It installs in the tubing that supplies water to the RO so you can sht-off the water going to the RO in case you need to service the RO... as you do now. If the tubing that supplies water to the RO is 1/4" PE then you need a 1/4" shut-off valve. If the tubing that supplies water to the RO is 3/8" PE tubing then you need a 3/8" shut-off valve. Home Depot carries them. Also. mind what I said about a saddle valve. If the line supplying water to the RO is hooked up with a saddle valve REPLACE it with a conventional connection. Saddle valves will leak sooner or later and are a giant water leak waiting to happen. If any of this confuses you, then get help. This is important.