SEAL RING

734 118 48 RING, SEAL this little guy is what keeps the oil from going where it shouldn't. You'll find these in a few spots, but mainly they're sealing up a cylinder rod or piston, or maybe a rotating joint, making sure the hydraulic pressure actually does its job instead of just bleeding off. It's all about containing that fluid so your rig moves or hammers like it's supposed to.

When one of these seal rings starts to give up the ghost, usually what happens is you'll notice a slow weep of hydraulic fluid, maybe around a cylinder rod or a swivel. If it's internal, like a piston seal, you won't see the leak, but you'll definitely feel it. The cylinder might start drifting, or you'll get inconsistent pressure readings, making your feed or rotation act sluggish or just plain weak. Sometimes you'll even hear a slight hiss if it's a high-pressure internal bypass.

When you're swapping one of these out, don't just yank it and slap a new one in. Always give the bore and the rod or shaft a good once-over for any nicks or scoring. That's usually what tears up a new seal in no time flat. And for crying out loud, make sure you're using the right installation tools or at least being super careful not to pinch or cut the new seal on any sharp edges during assembly. A little grease on the seal itself helps a lot too.