Design/Safety Factors for Hydraulic Cylinders 3

[geirkvaale]

Hi,

Hope somebody can help me with this.

What safety factors are most common for hydraulic cylinders? Especially for Europe, so refference to an EN standard would be great.

So far I have just found the following factors to use:

Pressure test at 1,5 times rated pressure (ISO 10100)
Yield strength 2 times calculated stress (ASME B30.1)

Have also bought a copy of EN ISO 4413, but it doesn't say anything about the safety factors - just general requirements like "should be safe to use and be designed for the rated pressure..." etc.

What kind of safety factor should be used with regards to tensilie strength? Tensile strength 3 times calculated stress?

All help is very much appreciated.

 

[micalbrch]

If ISO 4413:2010 did not provide that information, I would guess that there isn't a specific standard. But design pressure = 1.5 x max. operating pressure seems to be sufficient safety factor.

 

[hydtools]

Many hydraulic components are designed 4:1, failure to design or rating

Hydraulic jack components are generally designed 2:1.

Other customer- or industry-specified factors may be 5:1 or 6:1 depending on application.

Not aware of specific standards for design factors.

Search component manufacturer literature for possible references.

Ted

 

[geirkvaale]

Thanks for very helpful answers...

The cylinders we make are only used in a specific application (cold forming of metal - failure other than burst is not critical in any way) There are basically no dynamic/impact loads. We have safety PRV on the pump supplied with the cylinders, so it should not be possible to pressurize over the rated pressure. Each cylinders is operated max 1000 strokes before they are discharged so fatigue should not be an issue.

Based on this safety factors like 4-6 seems to be a bit overkill, if not clearly stated in any standards.
We will probably stick to factors 1,5 for FAT testing (each cylinder is tested) and 2 for computed stress then.

 

[IceStationZebra]

Hystat Systems talks about a 2:1 ratio in their literature, but doesn't mention any appropriate standard.

I didn't look at these standards in detail, but they are likely candidates.

BS EN 982:1996+A1:2008 - Safety of Machinery - Safety Requirements for Fluid Power Systems and their Components - Hydraulics

ISO 4413:2010 - Hydraulic fluid power - General rules and safety requirements for systems and their components

Pressure Equipment Directive (97/23/EC)
[I don't think this applies, but not sure]

ISZ

 

[geirkvaale]

Thanks Zebra.

I have previously looked into all the standards you mentioned:

EN 982 is apparently withdrawn and replaced by ISO 4413.. ISO 4413 has no clearly stated factor to use.

PED (97/23/EC) has no factors to use either, and doesn't apply either, since we are covered by the machinery directive and product of volume and pressue is below a certain value.

But all good tips