OIL LEAKS FROM VALVES (Change the O-rings)

If you've got oil leaking out from the bottom of a valve, or between valve stacks, tightening the bolts wont do anything !!!

The o-rings do the sealing, you wont stop the oil leak unless you change the o-rings.

When you fit a new o-ring, it should sit in the recess so it doesn't fall out, and just sit slightly above the surface, if the o-ring is too big it will get too squashed, and it wont seal against pressure.

The correct size o-ring will end up as a slight oval, not a flat disc !!

(15% to 30% squeeze)

A bit of maths....

There are 4 ports on a CETOP 03 size valve, after the o-rings are fitted, there's about 10mm left in the centre of each port.

So each port has an area of 5*5*Pi = about 80mm2

1 port is to tank, so the other 3 ports add up to 240mm2 of area.

If you've got 200 Bar pressure, that's 20MPa or 20,000,000 Pa or 20,000,000 N/m2 which is a big number until you convert it to N/mm2 which is just 20 N/mm2.

The biggest force that could push the valve up is therefor 240mm2 * 20N/mm2 = 4800N (about 480kg)

You've got 4 M5 cap head bolts holding the block down, and if they're tight that's all you'll need, as each one will take over 500kg.

Now let's have a leak.........

If you have a leaky seal from one of the o-rings, due to the wrong o-ring, or a crack due to age, etc.

The oil at 200 Bar goes under the block, and for each 1mm2 it covers it adds an extra 20N or 2kg of upward force.

The area inside the bolt holes on a CETOP 03 valve is about 40x30=1200mm2, so it soon adds up to a lot of force, and you'll get a leak.

When you tighten up the bolts to almost breaking point, all you are doing is trying pull the valve block through the base plate, which wont work.

Change the o-rings.

O-rings (Imperial Series)

Depth of recess under valve Cross section of O-ring Sticks out (Gets squeezed by..)
1.4mm 1.78mm 0.38mm (20%)
2.2mm 2.62mm 0.42mm (16%)
2.9mm 3.53mm 0.63mm (17%)
4.5mm 5.34mm 0.84mm (15%)
6.0mm 7mm 1.0mm (14%)

O-Rings (Metric Series)

Depth of recess under valve Cross section of O-ring Sticks out (Gets squeezed by..)
1.6mm 2.0mm 0.4mm (20%)
2.0mm 2.5mm 0.5mm (20%)
2.4mm 3.0mm 0.6mm (20%)
2.9mm 3.5mm 0.6mm (17%)
3.4mm 4.0mm 0.6mm (15%)
4.0mm 5.0mm 1.0mm (20%)