Hose breaks and cylinder drops 1

[Manyletters123]

Recently I came across a machine that had no form of protection in the hydraulic circuit to prevent the cylinders from falling. When the manufacture was contacted they told me that: "How ever due to the size of the port relative to the volume of oil in the cylinder it won't move very fast in either direction".
Well not much sense in talking with them, however I have not found anything on line that I can understand due to my limited math skills, but I'm pretty sure 2 cylinders with 8" bore x 2-1/2" rod and 192" stroke might just come down much quicker than "not very fast".
System pressure when lifting these up is as high as 2800 psi. Tomorrow or the next day we are going to remove the hoses and measure the diameter of the hole drilled in the barrel and record the hose size and will return to this forum and let the world know what they are.
Looking for an answer in units of time and doesn't need to be accurate to milliseconds if you know what I mean.
Thanking anyone in advance,
Manyletters123

 

[HPost]

It is not possible to give an accurate value until we know the size of the hole in the fluid port.

The velocity of the cylinder will be Q/A, where Q is the flow rate and A is the cylinder area.

The flow rate is function of Cd x A x SQRT (2 x Delta P / Fluid Density)

Cd is the orifice coefficient (0.82 for through hole)

A is the area of the hole

Oil Density is approx 835kg/m^3 (needs converting to imperial units)

The delta P in your case 2800 PSI - Atmospheric Pressure = 2785.5

Once you know the size of the hole, you can calculate the maximum velocity of the cylinder as shown above...with reasonable accuracy.

 

[hydtools]

The internal pressure will drop very quickly to near zero immediately after to hose breaks. Knowing the drop height will let you calculate the drop velocity and drop flow rate, v = sqrt(2*g*d). Ignoring friction. Or drop time will allow you to calculate velocity, v = g*t.

Do a search on velocity fuse to find flow stopping valves.

Ted

 

[PNachtwey]

This is one reason I like the valve mounted on the cylinder with energized open blocking valves or POCVs between the valve and cylinder.
Rubber hose between the valve and cylinder is a no-no for reasons stated. Rubber hose also makes controlling the press more difficult.


Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

 

[Manyletters123]

Today the unit was examined and the hole drilled through the cylinder wall is 1/2" diameter. The steel adapters threaded into the cylinder have a .390" (25/64") diameter and the hose fitting attached to it has a through diameter of 0.344 (11/32"). So if a hose broke these diameters would not change.
Thank those of you that replied to my request. As I began to try and calculate this speed, I am stumped by this "oil density" that must be converted to "imperial units".

I am well aware of using P.O. checks or counter balance valves for this type of application. We are trying to make the case that in the event of a hose failure, those who think they can get out of the way fast enough will not be able to.

 

[73lafuite]

For your values: 1 cylinder 203x63.5x4880mm, 196bar, hole ø8.7:
Q= 530l/mn. speed 0.3m/s, time for stroke 16.2s.
If you read 196bar on the pump perhaps you have less when the load go down.
If you have only 150bar: Q=463 speed 0.264 time 18.5

 

[3DDave]

You only need to know that someone who is distracted and in the way will be crushed or killed by the machine without regard to how slowly it descends. Speed just affects how large the cleanup area is.

 

[tbuelna]

You mentioned there are two similar hydraulic cylinders used. Are the hydraulic circuits connected to each cylinder isolated/independent of each other? This would provide functional fault tolerance in the event one cylinder were to experience loss of hydraulic pressure. I can't imagine the manufacturer would market and warranty a product that could cause injury or experience significant damage from a type of failure (like a burst hose) that seems relatively common.

What type of machine is this?

 

[chicopee]

If this is a new piece of equipment, make sure that there is no burrs in the connections and valves restricting the flow of the hydraulic oil.