How to install replacement packings
I guess you have found out how to do this by now, but if not its quite easy. These instructions apply to all the Graco St series II sprayers, so the repair kit (Graco # 244-194) contains all the parts to service these different sprayers and you may not need them all for your pump. The back of the kit shows the order in which the parts are installed. Follow it carefully.
The first thing to do is open the repair kit and squirt engine oil into the blisters that contain the packings so that the leather packings soak it up while you are working. Note that the kit will not use all the parts, as it is good for several different pumps, so you need to keep a careful watch on which parts you need.
You need to repack the pump with it held in a bench vice, so first remove it from the sprayer: Disconnect the pump output hose and the suction assembly, then push out the pin that holds the piston into the gearbox piston, slacken the locking ring and unscrew the pump.
Grip the inlet valve body (the lower tapered part) in the vice on the 2 flats. Unscrew the main body and set it aside, take the inlet valve housing out of the vice and remove the valve parts, noting the order of them; you will be reusing the valve seat and cage.
Put the main body upright in the vice and remove all the parts: Unscrew the brass packing nut and tap the piston out with a suitable tool, taking care to catch it. Remove the top packings and the O-ring on the end that goes into the inlet valve housing, clean the pump body including the outlet connection, and inspect the inside of the cylinder to check that it is not scored; if it is, you will have to replace it otherwise the scores will tear up the new packings.
I always keep the old packings in a stack to check the order and number of them when I install the new ones later.
Now remove the packings from the piston, keeping the parts together to check the right order when you install the new ones. There's a drawing on the back of the kit but having the real ones on the bench is a helpful check.
Clean the piston rod and check that the end that goes through the top packing is not scored and replace it if necessary. Rebuild the packings onto the rod being careful to use the correct spacer that goes on first; the thick one is for the rod that does not have a wiper at the other end. Do this with the flats in the end of the rod gripped in the vice. The packings must be installed so that the outer lips face up towards the end of the rod with the hole for the piston pin. The packings are three plastic and two leather between them supported at both ends by spacers. Before screwing in the outlet valve housing (the stud) that keeps the packings in place, check that the valve seat is OK, then install the wiper ring if there is one on the stud with the lips facing the opposite way from the other packings. Install the outlet ball and apply some Locktite on the screw threads and screw in the stud until it is firmly tight (Graco says 3 ft-lbs if you have a torque wrench).
Install the packings into the pump body, taking care again to get them in the right order with the lips facing down into the pump (this will be against the fluid pressure). Install a new O-ring on the brass nut and screw it in until it just contacts the packings but does not compress them. Turn the body upside down in the vice. grease the top couple of inches of the piston and push it through the packings. You will have to tap the rod through. Now tighten the brass nut; it is tricky to get the torque right so if you have a torque wrench tighten to 5 ft-lbs or an extra 1/2 turn from hand tight. Don't overtighten as this will accelerate wear and under tight leads to leaks. Install a new Teflon O-ring on the body end that screws into the inlet valve housing.
Now service the inlet valve and its housing. Remove the Teflon O-ring that sits under the inlet valve seat and the thick washer inside where the suction assembly goes. Clean all the parts thoroughly including the valve seat and cage. Examine the valve seat land where the ball will sit to ensure that it is not pitted; if it is you can turn it over to the other side if that is OK, otherwise you will need a new inlet valve seat. Install a new O-ring that goes in the groove under the valve seat.
With the inlet valve housing gripped on the 2 flats, in the vice, install the inlet valve parts; first the valve seat, then the new inlet ball and finally the valve cage with the legs downwards around the ball. Grease the threads on the end of the pump body and the O-ring on the end of it. Screw the body into the inlet valve housing and tighten it firmly but not too much (the seal does not depend on it being tight)
Now install the pump section into the gearbox housing. When it is in far enough, the top of the pump body will be about flush with the inside of the hole that it comes through. Now install the piston pin; this is tricky as you need to line up the hole in the crank piston, with the hole in the rod, so you may have to first screw in the body too far and rotate the rod inside it before you can push in the pin which requires that you also lift the retaining spring. Once the pin is in place, rotate the pump body until the top is just flush with the inside of the bottom of the gearbox housing, then tighten the locking ring. Reinstall the outlet hose and inlet suction assembly.
Jul 15, 2014 |
GRACO INC 390 Stand Airless Paint Sprayer