### Author Topic: PSI  (Read 494 times)

#### artguy

• Medium Cheese
• Posts: 36
• Cheeses: 4
• Default personal text
##### PSI
« on: January 14, 2014, 10:41:14 PM »
Ok so I stumbled upon a thread with some awesome conversion charts and formulas for converting physical pounds to psi for pneumatic presses.  I cannot for the life of me find the  thread again!  I want to be able to convert lbs to psi.  My cylinder is 2" bore with 9" stroke and my mold is 6.5"x7".  Any help?

Cheers

Guests, join the CheeseForum.org community to remove this ad.

#### smolt1

• Mature Cheese
• Location: oregon
• Posts: 151
• Cheeses: 13
• Default personal text
##### Re: PSI
« Reply #1 on: January 14, 2014, 11:21:19 PM »
There are 2 parts to this.

The cylinder converts the pressure( PSI ) in the tank to a force( LBS ) on the plunger . The plunger then presses( with force in LBS ) on the mold which is distributed over the surface creating a pressure ( PSI ) on the curds in the mold.

The formula for the mold is:   pressure ( in PSI ) = force ( in LBS ) / area( in square inches ) of surface of mold.

#### jwalker

• Old Cheese
• Posts: 646
• Cheeses: 66
• I thought I was indecisive , now I'm not so sure!
##### Re: PSI
« Reply #2 on: January 15, 2014, 05:03:54 AM »
A 2" cylinder has an area of approximately 3.14 square inches , length of stroke doesn't matter.

So just multiply the air pressure used , by the bore size (3.14") , and you have total force exerted on cheese.

100 psi x 3.14 = 314 lbs of total downward force on the cheese (when using 100 psi).

A 7" mold has a surface area of approximately 38.5 square inches.

Total force (314 pounds) divided by 38.5 = approximately 8.155 pounds of force exerted on each square inch of cheese , or 8.155 PSI.

If you figure out the force exerted at 100 psi air pressure , then the rest is easy , using 50 psi air pressure , would give you half that ,  25 psi would be one quarter of that and so on..........

Area calculator is  (a = pi * r2) .

No..........I'm not a professional CheeseMaker , but I play one on TV.

#### artguy

• Medium Cheese
• Posts: 36
• Cheeses: 4
• Default personal text
##### Re: PSI
« Reply #3 on: January 15, 2014, 10:53:58 AM »
Can you give me an example if per say I am reading a recipe and it says  use 20 lbs of physical weights? Trying to wrap my brain around the process of converting physical pounds to determine what I should set the regulator to given the volume of the mold.

#### smolt1

• Mature Cheese
• Location: oregon
• Posts: 151
• Cheeses: 13
• Default personal text
##### Re: PSI
« Reply #4 on: January 15, 2014, 11:38:52 AM »
In many cheese making books it says press with 20 lbs without saying what size mold. In those recipes the assumption is that you are making a 1 or 2 gallon batch and the mold size is 4 or 4 1/2 inch diameter mold. So that recipe would NOT give you the correct PRESSURE if you made a larger batch and used a larger diameter mold.

With your cylinder( 100 PSI gives you 314 lbs ) to get 20 lbs ( of weight not pressure )  you would need  100 x 20/314 =6.37 psi on the pressure gauge.

« Last Edit: January 15, 2014, 12:57:25 PM by smolt1 »

Guests, join the CheeseForum.org community to remove this ad.

#### artguy

• Medium Cheese
• Posts: 36
• Cheeses: 4
• Default personal text
##### Re: PSI
« Reply #5 on: January 15, 2014, 12:22:31 PM »
Makes sense.  Thanks!

#### jwalker

• Old Cheese
• Posts: 646
• Cheeses: 66
• I thought I was indecisive , now I'm not so sure!
##### Re: PSI
« Reply #6 on: January 15, 2014, 12:23:29 PM »
Yep , what Smolt said !

But this might be an easier way of remembering and adjusting it:

Every 1 psi of air pressure , gives you 3.14 physical pounds of downpressure (with your 2 inch cyl.) , so 20pounds , divided by 3.14 equals 6.36 , or close enough to what smolt said.

Take any physical weight you are planning on using , and divide by 3.14 and you will get the needed psi to achieve that weight.

No..........I'm not a professional CheeseMaker , but I play one on TV.

#### artguy

• Medium Cheese
• Posts: 36
• Cheeses: 4
• Default personal text
##### Re: PSI
« Reply #7 on: January 15, 2014, 12:27:52 PM »
but dont I have to take into consideration the diameter of the mold?

#### jwalker

• Old Cheese
• Posts: 646
• Cheeses: 66
• I thought I was indecisive , now I'm not so sure!
##### Re: PSI
« Reply #8 on: January 15, 2014, 12:50:24 PM »
but dont I have to take into consideration the diameter of the mold?

Yes , but only if you want to know the PSI exerted on the cheese , that last calculation only gives you the total weight exerted and psi needed to achieve it.

A 7" cheese has about 38.5 square inches , 3.14 divide by 38.5 = .08

so every 1 psi of air you use will give you .08 psi on a 7" cheese.

It sounds complicated .

No..........I'm not a professional CheeseMaker , but I play one on TV.

#### artguy

• Medium Cheese
• Posts: 36
• Cheeses: 4
• Default personal text
##### Re: PSI
« Reply #9 on: January 15, 2014, 01:05:04 PM »
so how do I accommodate?  Do I have to multiply by a factor of .02 and add it to the original weight?

Guests, join the CheeseForum.org community to remove this ad.

#### artguy

• Medium Cheese
• Posts: 36
• Cheeses: 4
• Default personal text
##### Re: PSI
« Reply #10 on: January 15, 2014, 01:07:40 PM »
so if the recipe calls for 20 lbs of weight and I am using a 7" wide mold with a 2" bore. I will need 6.5 psi?

#### artguy

• Medium Cheese
• Posts: 36
• Cheeses: 4
• Default personal text
##### Re: PSI
« Reply #11 on: January 15, 2014, 01:18:31 PM »
or do I multiply by .92 and add that as a correction factor?

#### artguy

• Medium Cheese
• Posts: 36
• Cheeses: 4
• Default personal text
##### Re: PSI
« Reply #12 on: January 15, 2014, 02:08:58 PM »
Could someone double check my math hear?  This is based on surface area of 4" and 7" molds on a press with a 2" bore

#### artguy

• Medium Cheese
• Posts: 36
• Cheeses: 4
• Default personal text
##### Re: PSI
« Reply #13 on: January 15, 2014, 02:10:18 PM »