Sunday, March 2, 2014

Checked Valves

The upper helm wheel started turning rapidly to starboard and didn't stop. I stared at it with a sinking feeling in my gut. No it wasn't poltergeists trying to scare me, it's the new autopilot pump that's doing the dastardly deed. I knew what was causing the problem. Crud in the hydraulic system was holding a check valve open, and I didn't know exactly how to fix it. That wasn't quite true, I could fix it if I could get to the check valves. But where were they?

I had just finished a new autopilot installation on the boat, and was cycling the pump from starboard to port and back again to purge the lines to the pump. All of a sudden the wheel started to spin clockwise.

The first problem of where they are located is solved by having a conversation with Teleflex's techs and receiving a drawing. The check valves are hidden behind the hydraulic port fittings.

On most hydraulic helms, the check valves are separately accessed on the sides of the helm, but not this one. Armed with lots of paper towels, some red Solo plastic cups and a collection of wrenches the old copper line is removed. Leaking liquids are mostly collected and the fitting is removed. The word is yuck. There is all sorts of nasty detritus on the bottom of the fitting.

What I can now see is the check valve cover, and it's not going to win a beauty contest either. What's worse is the pipe thread sealant has dried out through the years and is hard as granite. This translates to lots of small sharp shards of sealant are embedded in the threads and have to be tediously extracted. Hush now, after clean up I'm going to use Teflon tape as the sealer. Don't tell anyone.

Here are the pieces after I've cleaned them up. The check valve is a simple device and requires very high precision tolerances to work properly.

That little tiny piece of black plastic I pointed to in the photo was inside the check valve, and that is all that would be needed to stop the little valve ball from properly seating. The other crap in there was possibly causing the problems also.

What is really happening is the helm is a pump. When you spin the wheel a rotating cam is depressing a circular ring of small pistons. Actually in this case the pistons are rotating under the cam. Each piston pumps a small amount of fluid which pushes the ball out of the way to get to the cylinder. When you stop turning the helm, the spring pushes the ball back into place.

Since crud was stopping the ball from fully seating, when the autopilot pump turned on, fluid was allowed to squeeze past the ball, and turn the helm. This also meant that the rudder wasn't being moved while this was happening. I can aver this is not a good thing to have happen to your steering system. Even without the hydraulic autopilot pump issue, the incorrectly operating check valve will allow your rudder to wander, causing more steering corrections, and in extreme cases complete loss of steering.

After cleaning up the two check valves up top, and putting everything back together I give the autopilot another try. Good, starboard works, but port still doesn't. Huh? The wheel isn't turning. I take a quick look at the lower helm, and the poltergeists are now turning that helm wheel.

With a sigh I go down and look at the lower helm. The upper helm was easy, because I could easily move the old copper tubing out of the way. Down here, not so much.

I know it's the right port that's the problem, and with some grief, free the straight piece of copper enough to get the check valve out. It's not as dirty, but it's bad enough. It gets a stern talking to and a clean up. I run up and check the autopilot, and all is well.

When you work with old copper tubing you have to be very careful. The straight piece was hard enough to remove, but I would have likely ended up crimping the "S" curved piece trying to remove it alone. There is another issue with the plumbing. There are two flexible hoses that feed the steering cylinder aft. The casing of one of them has developed a crack. It's not leaking.... yet, but it will at some most inappropriate time in the near future.

Since the steering cylinder is the lowest point in the boat, when I replace the hoses, I'm going to drain the entire system and pass it through a fine filter to remove any solids from the fluid. It's gungy looking, and my instincts say there will be a surprising amount of not needed stuff in the filter when I'm done. With the system empty, I will then go back and remove several lines to make it easier to get that "S" shaped copper piece off, and clean that check valve also.

The auto pilot works well, but you can see the helm wheel give a tiny jerk every time the autopilot pump changes direction. After draining and refilling we will see how it goes. I may have to get new, and stronger springs in the long run.

1 comment:

  1. Interesting point for me here is that the captured ball bearing and spring arrangement is how you set the oil pressure in an Atomic 4. The spring steel can fatigue over the years (and all Atomic 4s are now venerable), and you need to replace them or your oil pressure will tumble as it warms up. As I recall, the spring is question is a "Chrysler yellow" and is still obtainable.


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