The steering is the Hynautic brand, and old and proven technology. It’s hydraulic. There is a reservoir, two helm stations which are in fact manual pumps operated by the wheels, and the autopilot pump (not shown). There is a fluid reservoir with a pressure head. It all operates a hydraulic piston/cylinder that moves the rudders.

Here’s what the system looks like.

The little box with “screws for purging” are the pressure relief valves. (MSV21 is the model) Their job is to relieve the steering pressure should you exceed 950 !!! psi. Yes that’s a lot. There’s a reason we use hydraulics when there’s large forces needed. By releasing them the bypass pressure is a lot lower and by spinning the wheels many turns in both directions, in a proper sequence, you can circulate fluid in the system at a larger rate, so air ends up in the reservoir. The reservoir is filled with fluid, 1/2-2/3 full, and then gets a 25-30 psi pressure head on it. (air…. with a bicycle pump). The autopilot pump (not shown) is teed in just like the helm pumps. The number in the chart is the supposed number of turns hard over to hard over.

The autopilot pump was defective and I had it replaced by the professionals, in the interest of time. (Boat was for sale at this point) After that the lower helm wasn’t working right (air in the system). Many turns with occasional movement. They hadn’t bled it properly. But, they sort of washed their hands and told me in not so many words I was on my own as the piston was leaking a little when hard over. They had a point, sort of. Unfortunately they were electronics people and didn’t want to mess with the hydraulic end of it. I discovered all this during the sea trial for the sale to the next owners….. Wide open throttle doing 20 knots with dodgy steering. Hee-Ha! Made it work.

So I proceeded to attempt to bleed the system myself, as per the ancient procedure:

There is one VERY salient detail that took me a few to get my head around. In the diagram there is a “T” at the PRV. On my setup there was a hose that went to the piston. In fact, unlike the diagram there are TWO hoses on each end of the piston, which sent me down a “supply/return” rabbit hole. WRONG. The piston IS the “T”. One side is supply, one port one starboard, the other hose on the same side is the relief hose to the PRV.

Except it all wasn’t working as advertised. To SB the helms (both) were hitting the stop, and not spinning endlessly. So, it appears that the pressure relief valve was not working. It’s a simple thing, (static) hydraulic pressure in, one from each side, and a pressure loaded relief valve, one per side. When pressure on either side exceeds 950psi, the valves opens and pressure is relieved and the fluid sent back to the reservoir. When you release the screw/nut combo the pressure on the spring decreases and the valve opens at a much lower pressure. This allows you to turn and turn the wheels without running into a stop as it keeps bypassing. The side effect is that you are circulating the fluid through the system, and any air is trapped in the reservoir. But, even with the valve released I was hitting the stops, ergo that valve was not releasing. (You can feel the pressure releasing when you back out the nut/screw combo, sort of. With your arm bent into positions you don’t normally assume it’s hard to feel anything).

Between the sticky valve and the slight high pressure leak of the piston I decided it was time to rebuild/replace as needed.

So, here is the steering ram under the bed. Nice and accessible. Note the slight “bleeding” on far end.

On the business end there is a large pin that comes out easily to disconnect from the steering. Access through port bedside lower drawer.

Then it’s a matter of removing the 4 bolts that hold the ram in place:

Disconnect the hoses and get them over a bucket. (I let the pressure off the reservoir). Doesn’t take a lot of blood to look like a crime scene…… 😉

There, all cleaned up:

Meanwhile this is the MSV21 pressure relief valve.

And to confirm, we are looking at a Hynautics K22……. with what could be a 1978 date…..

So….. You can send it out to be rebuilt, $400 plus shipping plus time…….unknown. But the rebuild kit is available, KS04, for pre 8/83…. Plenty of vids on YouTubeU and it’s not too complicated, except for a tool that needs to be fabricated to remove 4 “special” nuts….

These 4 nuts go on either end of the rods that tie the ends of the piston together. They are round and flush and have two notches to set a tool into. YouTubeU shows how you can fabricate it out of a small socket. (1/4″ drive, 5/16″.)

A small vice grip GENTLY on the rod to hold it. This is brass, you have to go easy on everything. Picture shows torque wrench on assembly….. (75 INCH pounds of torque.)

And here it is all apart. Reverse the process on assembly replacing the seals/o-rings etc. I used some fluid to lube it all and keep it from having to run dry.

I got a new MSV-21 mail-order. Let me save you some potential headache here. There are various instructions from various time periods floating around on these proceedings. (I showed the one closest to my build date for the bleeding procedure). The fittings on the MSV-21 are 1/4″ NPT. Some instructions say not to use sealant. Some say that you can and to use XYZ. I did not use any, put it all together and……. it leaked. Never even got to the high pressure side, the return leaked at 40psi. So I called Hynautic/Dometic and talked to the guy that has been there for a long time and he said: “Use sealant”. I settled on Locktite 545 which is a hydraulic/pneumatic sealant. Takes 24 hour to cure at 70ºF, at which point it looked a lot like what I took apart. (Yeah, that was sealant not dirt….lol)

After all that things fell nicely into place. Here is the cylinder shown back in, as well as the new MSV-21 back in it’s spot.

Then the bleeding procedure worked flawlessly. After pressurizing the reservoir I opened the bleed screws on the piston to get the air out of it and then refilled and re-pressurized the reservoir This got rid of most of the air that I introduced into the system. Did the 40 turns port/starboard at all stations top to bottom as described, refilling the reservoir once more and after that tightened the pressure relief valves and viola……. proper steering and no leaks. I’ll take it.