# How to Calculate Platen PSI  ### Viviane Schute

Cannabis enthusiast and student of the art of solventless extraction

It seems intuitive to many beginners in rosin extraction that more pressure produces better results. But we quickly discover that in reality this just isn’t the case. When it comes to pressing rosin, more is not always better. Sometimes less is more.

Pressing high grade rosin requires exerting just the right amount of pressure onto cannabis source material. Too much pressure and you risk equipment failure and reduced oil flow efficiency. Too little pressure and you end up overcompensating with excessive temperatures and evaporating away terpenes.

Achieving the correct level of pressure during solventless extraction frees cannabis to unlock that unique expression of cannabinoid and terpene-rich oil we know and love as rosin. So how is pressure measured, and how can I know the actual amount of pressure inside my rosin bag?

How is pressure measured?

The level of pressure we need to control during extraction is not the same thing as how many tons of force we apply to the plates, or the output reported on the gauge of your hydraulic press. Measuring the pressure exerted on your cannabis starting material as pounds per square inch (PSI) is the most effective way to convey actual pressure generated during rosin extraction. Measuring platen PSI gives us the clearest reading of actual pressure on your source material inside the rosin bag.

Calculating platen PSI requires a measurement of the dimensions of your rosin bag (area in square inches) and the tonnes of force being applied (in pounds). PSI is the relationship between the dimensions of your rosin bag and the tonnes of force being applied. Platen pressure tells us how much pressure is being exerted onto the source material. Platen pressure = pounds of force exerted / area of rosin bag. The area of your rosin bag is a simple length x width calculation. The pounds of force exerted requires a couple additional steps, including calculating the area of the cylinder and reading your pressure gauge on your hydraulic or pneumatic press. Here is an example:

Let’s say we’re using The Press Club’s 2x4inch rosin bags. To find the area in square inches, multiply the length and width of the bag (2inx4in = 8 inches squared).

Next, we need to determine the tonnes of force applied and convert this into pounds. Gauges on hydraulic and pneumatic rosin presses reflect the internal pressure within the equipment and not the total pressure output. To find the total pressure being applied, we need to know the pressure reading on the gauge (in psi) as well as the area of the press’ cylinder. We multiply the two in order to calculate total pound force (LBF).

Let’s say we’re pressing at 120 psi. The area of our cylinder is 64.9 square inches. Therefore, our total pound force is 64.9 x 120psi = 7788 LBF.

Also keep in mind this important conversion: 2000 LBF’s = 1 ton.

So this means that we’re pressing around 4 tons of max force with this setup. Let’s assume we’re using ¾ of this hydraulic press’ capacity, which means we’re working with 3 tonnes of force. 3 tonnes = 6000 lbs.

Remember, the platen PSI = pounds of force / area of bag. So, our final platen PSI is:

6000lbs of force / 8 inches squared = 750 platen PSI

So now we know how to calculate platen PSI, what pressure ranges do we want to target when pressing rosin?

How much pressure to apply depends in large part on the source material you’re using. It’s generally recommended that bubble hash is pressed at a lower PSI than flower. The ranges we recommend are:

Flower: 1200 - 2500 PSI Bubble
Hash: 700 - 2000 PSI

Conclusion:

Knowing the amount of pressure applied to source material during extraction is much more powerful than simply knowing the tons of force being exerted or the psi of the press itself. Now that you know how to calculate your own platen PSI, you can better measure and control this critically important variable in the extraction process.