How to Calculate Flow Resistance for Liquids

Lohm Rate Versus Orifice Diameter

Lohm Rate Versus Orifice Diameter

Water Flow – Lohm Rate Formula

The Lohm has been selected so that a 1 Lohm restriction will permit a flow of 100 gallons per minute of water with a pressure drop of 25 psi at a temperature of 80°F.

Where:

I = Flow rate (gallons per minute)

H = Differential pressure (psi)

L = Lohm rate, a measure of resistance to liquid flow. It includes all density, viscosity, Reynolds number, coefficient of discharge and area units (Lohms)

Water Flow – Examples

Problem 1. What restriction will permit a flow of 1 gallon of water per hour at 50 psi ∆P?

I = 1/60 = 0.0167 GPM

Problem 2. A jet with an approximate hole diameter of 0.012 of an inch flows 18 lb/hr of water at 100 psi ∆P. What is the restriction?

Problem 3. What ∆P will be required to flow 20 GPH of water through a 2000 Lohm Jet?

Problem 4. What water flow will result from a restriction of 500 Lohms and a ∆P of 500 psi?

NOTE:

For special flow requirements, contact your local Lee Sales Engineer to determine the required Lohm rating.