What psi could a 4" bore cylinder handle? Specs are: Foot mount cylinder, with a 3" stroke, single acting spring extended, 1/8" wall brass tube, 3/8" 303 stainless steel tie rods.

P = \frac{2ST}{O - 2T}

Where:

P = Bursting Pressure (PSI)
S = Material Strength (PSI)*
T = Pipe Wall Thickness (in)
O = OD of Pipe (in)

*Ultimate Tensile strength of brass = 50,000psi for medium leaded brass

P = \frac{(2)(50000)(0.125)}{4.25 - (2)(0.125)}

P = 3,125psi

That would be the bursting pressure of a brass pipe with an OD of 4.25 and an ID of 4.00. Safe working pressure should be somewhere around 2,100psi.

Could you draw a diagram of what your intended use would be, then I could provide you with more info.

The hydraulic cylinder I want to use can be viewed at Cylinders and Valves Inc., Small bore cylinders and accompanying valves. (http://www.cylval.com), page 20, figure 1 (4000F). The application it will be use for will peak out at 375 PSI hydraulic. I just want assurance that this would work. Thanks

I know that I referred you to the catalog. However, the catalog does not specify that the thread on the tie rods (4 or them) is 3/8 - 16" . That may be the weak spot. Please advise.
Thanks

Would this be the right image http://www.cylval.com/pdfs/3000-4000series.pdf ?

With an assembly like that, you have a lot more to consider. Where ever you have two pieces of metal joined, you are going to have a weak point. You also have to consider that the stainless rod can only handle so much pressure before it bends. You may also consider the nitrile rings around the piston as a weak point.

The unit is only rated at 150psi working pressure. It probably handle a few peaks at 375psi as long as they are short, but I wouldn't recommend it. If you're up for the money you could buy two, and test one at 400psi still, and then working. Even if it rates okay, then you will increase its wear and tear immensely.