# How is CV rating calculated?

## How is CV rating calculated?

Cv by definition is the number of gallons per minute (GPM) a valve will flow with a 1 psi pressure drop across the valve. For example a valve with a Cv of 10 will flow 10 GPM with a 1 psi pressure drop. The formula used to select the valve Cv with the specified differential pressure is: Cv=GPM/((SQ RT(P)).

## What is the difference between nominal and inside diameter?

Nominal Pipe Size (NPS) is a North American set of standard sizes for pipe. The term nominal refers to pipe in non-specific terms and identifies the inside diameter with a non-dimensional number. The difference between the inside diameter (ID) and the outside diameter (OD) is due to the thickness of the wall.

## How do you calculate nominal pipe size?

by the pipe NPS minus double the pipe wall thickness (which can be obtained from the pipe schedule). For example, for a 12 NPS (DN 300 mm) pipe, schedule 40, the OD and wall thickness are respectively 12.75 inches (324 mm) and 0.406 inches (10.4 mm). Thus: Pipe ID = 12.75 inches – 2 x 0.406 inches = 11.94 inches, or.

## Is pipe size OD or ID?

For sizes larger than 12-inch, NPS corresponds to the actual outside diameter. For each nominal pipe size, the outside diameter (O.D.) remains relatively constant; the variations in wall thickness affect only the inside diameter (I.D.).

## What is NB in size?

In the American system, the pipe diameter is known as “Nominal Pipe Size” (NPS) or “Nominal Bore” (NB). For example, a pipe with a 12 inch NB (DN 300 mm) has an OD of 12.75 inches, or 324 mm.

## How do I calculate pipe size?

The equation for pipe diameter is the square root of 4 times the flow rate divided by pi times velocity. For example, given a flow rate of 1,000 inches per second and a velocity of 40 cubic inches per second, the diameter would be the square root of 1000 times 4 divided by 3.14 times 40 or 5.64 inches.

## Does pipe size affect flow rate?

Flow rate varies inversely to length, so if you double the length of the pipe while keeping the diameter constant, you’ll get roughly half as much water through it per unit of time at constant pressure and temperature.

## What diameter water pipe should I use?

A 3/8-inch line is sufficient for lengths up to 250 feet; 1/2-inch line will deliver adequate water pressure up to 350 feet; and 3/4-inch tubing is necessary to run a 500-foot line.