# Pressure to lift a safety valve.

1. Nov 12, 2009

### tufferthandug

I'm not sure how to work this one...

The spring on a safety valve can be compressed 15 mm by a load of 700 kg. In it's working position the compression of the spring is 22 mm. The combined mass of the valve, spring and spindle is 17 kg. Valve diameter is 80 mm.

Determine boiler pressure when this valve lifts.

Would the load on the working position equal:

700/15=X/22

X= (700x22)/15

X=1026.7?

I'm not to sure where to start or where to finish this question. Do I add the mass of the spring valve on to X?

Then is it F/A to solve for lifting pressure?

2. Nov 12, 2009

### tufferthandug

My final solution? After reading a little more on Hooke's law.

Does this look correct? Here's my notes:

Compressed to 15mm by 6967 N.

F=kx so k=f/x 6867/15= 457.8 N/mm

F=kx 457(22-15) = 3199 N

Finding the weight of the valve assembly (17x9.81)= 166.77

I hope the solution comes from combining the two: 3199+166.77

Pressure = F/A F= (3199+166.77) A= .005 m2

Boiler pressure when valve lifts: 670 kpa?

3. Nov 13, 2009

### tufferthandug

No takers? LOL