Shimming the Extractor Cover

This is the first in an on-going series of maintenance tips for Hydraxtor equipment. I will try to answer many of the most common problems people have with these machines, and how to solve them as inexpensively as possible.

Perhaps the most common problem, as well as the most time consuming to fix, is blowing diaphragms at the top, usually about 1 inch from clamp ring. Take a look at your diaphragm the next time the machine is open. Is there what looks like a seam, just a little below the clamp ring? A small (less than 1/4 inch wide) ridge is quite normal, and will usually appear after about a month in service, if the machine is properly shimmed up.

However, many times this ridge is up to 1/2 inch and more wide, forms within a few dozen loads, and eventually breaks through. This is one of several signs that your cover is not properly shimmed.

Breech Ring Cross-sectionThis picture shows a cross sectional view of the top of a Hydraxtor tub, with the Diaphragm, Clamp ring, Cover and Breech ring installed. Note particularly the area pointed to by arrow A, which is the point where the cover sits atop the clamp ring.

Under pressure, the diaphragm folds up along the assembly. It pushes the cover up under extreme pressure; at the 400 PSI operating pressure of the Hydraxtor, the cover has over a million pounds pushing it up! If everything is properly shimmed, there is approximately .020 inch of play in the breech ring/cover assembly. All of this play becomes the gap between the cover and the clamp ring under pressure.

This is where the normal ridge will develop. Repeated pressure cycles force the diaphragm into that gap slightly, and the release of that pressure lets the cover drop back onto the clamp ring, often taking a small "bite" out of the diaphragm as it comes down. The more play in the system, the bigger the gap. The bigger the gap, the further the diaphragm extrudes into it, and the bigger the "bite" taken out of it when the pressure is released.

(Incidentally, this kind of failure is not covered under Tandem-Flow's diaphragm warranty. We consider it to be improper maintenance. Unfortunately for most of you, no one has ever showed them HOW to "properly maintain" this, which is why I'm writing this now.)

How do you know how big your problem is? Well, that will show up in your diaphragm life. If the ridge appears the same day you install the diaphragm, you have a serious problem - probably, your gap is approaching 1/4 of an inch, and is definitely past the 1/8-inch mark. But, I can almost hear some of you saying, there isn't any visible gap between the lug on the breech ring and the lug on the cover! How could this happen?

Several ways. Well, actually, one way. Wear. One or more items in the system that makes up the top of your Hydraxtor has worn. Possible areas are shown as items B (worn or missing wear bars, p/n 005-07440-00), C (worn lug on the breech ring), D (worn roller or groove worn in breech ring) and E (top of tub worn where breech ring mounts). The first step to solving the problem, though, is always the same. You must remove as much vertical play as possible from the breech ring.

Start by inspecting for wear at point D. If there is a groove worn in the breech ring, you can do one of two things, depending on the severity of any wear at point E. The easiest is to unbolt the brackets that mount the breech ring control cylinder and the breech ring limit switch to the breech ring, rotate the breech ring one "lug" to get the roller out of the groove, then re-attach the brackets in their new locations.

The second method involves adding a stainless steel shim to the bottom, to provide a new surface for the roller to ride on. This should only be used when there is so much wear at point E that you cannot take the play out of the breech ring in the next step.

Next, the 3 eccentric rollers under the breech ring need to be adjusted. This can be time consuming, but is very important. Disconnect the air from the Hydraxtor (if your machine is a model 501, substitute the word "hydraulics" for "air" in this discussion). One at a time, loosen the bolt holding the eccentric cam to the tub, and turn the cam to raise the roller, then retighten the bolt. The object is to get the roller as high as possible, yet still be able to move the breech ring by hand. You will need to go around the extractor several times doing this, as you will get closer to the maximum each time.

Once this is done, you can check the play by using a large screw driver or small pry bar, wedged under the breech ring, to try and lift it. If there is a noticeable amount of play, but you can not go any higher on the cams without wedging the ring, you need to take the breech ring off and clean the top of the tub - it is badly corroded. If, however, you reach the top of the eccentric cam and there is still free play, you need to add a shim to the bottom of the breech ring for the roller to ride on.

Once the breech ring vertical clearance is set, we can move on to the hard part, shimming the cover. This makes up for all the wear in the system. It is perhaps the most frustrating part of the job, since removing the wear bars can seem virtually impossible, due to the aluminum in the cover corroding around the stainless bolts that hold the wear bars in place. The bolts will usually fight you all the way, and the only "easy" way to do it destroys the wear bar.

Let's start by getting an idea of how much gap there is. Close the cover and lock the breech ring. Shut off the power to the machine so that it will not attempt to pressurize. Measure the spacing between the lug on the cover and the lug on the breech ring. This is the area pointed to by "B" and "C" in the diagram. The range that is acceptable is .010 to .020 inch, with .015 being ideal. You will probably find .125 inch or more if you've been experiencing diaphragm problems.

To get a rough idea of the number of shims you will need, new wear bars are 3/16" thick (.190 inch), and shims come in .010, .020, .030 and .125 (1/8") thick. You want to use as few shims as possible, for two reasons; convenience, and they cost between $2.15 and $3.25 each. Wear bars are $6.25 each, and the bolts that attach them to the cover are $1.25 each. Mark the estimated shims required on the cover, next to the lug, for later use. Unlock the breech ring and lift the cover.

In order to shim the cover, you must remove the two bolts which hold from each wear bar down, coming up from underneath the cover lug. They are socket-head cap screws, a fancy way of saying they take an allen wrench ("hex key") to remove, in this case a 1/4". If you cannot remember when you last removed them, though, you probably won't be able to, due to the aluminum corrosion mentioned earlier. If this is the case, the FAST way to remove the wear bars is to cut the wear bar lengthwise with a band saw, then knock the halves out with a chisel. You can then drive the old bolts out with a punch and a LARGE hammer.

At this point, you will need a .020 inch feeler gauge, or an extra .020 shim. You will be stacking your best guess at the shimming on to each lug made during the first measurement. Start with the shims originally in place, or add their thickness to new stack. After you have replaced all wear bars and shims, and tightened the bolts down to hold them in place, close the cover and breech ring again.

At each lug, try inserting the feeler gauge (or .020 shim) between the cover and breech ring lugs. If it slips in with difficulty, or doesn't go in at all, try inserting a .010 gauge or shim; if it fits easily, you've finished this lug.

If the .010 doesn't fit either, you need to remove .010 from the stack of shims on this lug. This is a rare occurrence, though; usually, if the .010 doesn't fit, you won't be able to close the ring by hand due to interference.

If the .020 gauge is sloppy, you need to add more shims to this lug until it it is within the .010-.020 tolerance.

Getting ALL of the lugs within the same narrow range is especially important for those of you running machines with the old "sand cast" breech rings and covers. These are distinguished by the breech ring being hollow. If the clearances aren't even, the varying stress on the lugs causes a slight twisting action, which will eventually cause either the cover or breech ring to break under pressure.

Usually the parts go straight up, but they WILL damage the ceiling, and likely scare anyone around. We've had a 350 pound cover come unlocked on our test stand at 400 PSI, and it was thrown 6 feet vertically and 8 feet horizontally. The witnesses said it flipped over twice in the air, and the "phuwhoomp!" sound was heard in the office, over a hundred feet away!

One last hint on the shimming - when you reinstall the wear bar bolts, you should coat them with a good water-resistant grease. This slows down the corrosion of the aluminum, and will make it easier to remove the bolts the next time you have to re-shim. And re-shimming should be considered a once-a-year maintenance item. The first one will be the most time consuming and expensive, though, simply because it is so far off when you start.

NOTE: Greasing bolts reduces the required torque to achieve the same tension. The tension value is what you're really looking for when tightening a bolt; too loose, and the parts move, but too tight, and the bolt stretches, probably close to its failure point. This is an all-too-common misunderstanding, which will strip the threads out of tubs, or break bolts.

If a bolt has a torque specified, such as the 65-80 foot-pounds used on clamp ring bolts, it is assumed that the bolt is dry (no lube) when tightening. A greased bolt requires only one fourth of the dry torque value to be under the same tension.