# How to Convert between Air (Dry Air) Normal Liters per Minute (NLPM) and Pounds per Minute (PPM)?

I need to check the leakage of a product, the requirement is basically need to place a flow meter between dry air supply and the product, and apply a pressure of 100, 200, or 400 PSI, and ensure the flow rate reading on the flowmeter is less than 0.05 PPM or lb/min, indicating the leakage in the product is minimal.

Problem is, my flow meter only able to produce output in Normal Liters per Minute (NLPM), NOT Pounds per Minute (PPM). How do I convert the value in NLPM to the required value of < 0.05 in PPM?

• So sort your units as you are using meters, psi, liters, etc Then the conversion between litres (ie a volume) and pounds (mass) is via density. I would check that your air inlet is within the temperature range for the meter as well. Oct 21, 2021 at 7:51
• eh... by specifying a standard P and T, it means SLPM and NLPM are really units of mass flow for a given substance. Even though everyone refers to it as "volumetric", which misses the point of it IMO. So if you think of it as fixed mass (or fixed moles) per unit time, the conversion is straightforward. They define the standard conditions a little differently. See here en.m.wikipedia.org/wiki/Standard_litre_per_minute Oct 21, 2021 at 20:35