Properly sizing plumbing pipes for a vacuum pump ensures the pump’s operating pressure is high enough to maintain the required vacuum at the end of the pipe without pressure disruptions.
Certain types of vacuum systems require long lengths of piping between the pump and the operational head. For example, a pump or group of pumps may be located in a distant area to avoid noise or heat within a manufacturing or packaging area.
This blog explains how to calculate the right size pipe for a vacuum pump.
CALCULATING PIPE DIAMETER
Many factors contribute to calculating the right vacuum pump pipe sizing. These factors are related to each other in the Darcy-Weisbach equation, which can be used to calculate the pressure drop (ΔP) in a pipe:
ΔP=f•DL•2ρ•V2
In this equation, f is the Darcy-Weisbach constant (or friction factor), caused by the roughness of the pipe’s inner surface, D is the pipe diameter, L is the pipe length, ρ is the density of the fluid or gas being piped, and V is the flow velocity of the fluid.
The equation can be rearranged to determine any of the unknown variables, for example, the pipe diameter or length. From the equation, we can see that the length of the pipe will directly affect the pressure drop due to friction. In general, a larger diameter pipe or hose slows the flow rate and reduces friction losses, while ensuring a steady uniform mass flow.
AN EASIER RULE OF THUMB
Rather than relying on the formal equation, it’s possible to get a “close-enough answer” to the correct sizing of pipes by using an easier approximation. Typically, the diameter of the vacuum inlet port is the diameter of the plumbing to start with.
The following rule of thumb can be used for sizing most applications:
VACUUM INLET PIPE SIZE
- Maintain the pump inlet size for the first 100 ft. of pipe
- Increase the diameter by one increment for each additional 100 ft. of pipe
So, for example, if the pump inlet is 2 inches in diameter, use a 2-in. pipe for the first 100 ft. and then increase the pipe size to 3-in. diameter.
VACUUM EXHAUST PIPE SIZE
- Maintain the exhaust pipe diameter equal to the exhaust port size for the first 30 ft. of pipe
- Increase the diameter by one increment after each 30 ft. of pipe
For example, if the exhaust outlet is 2 inches in diameter, use a 2-in. pipe for the first 30 ft. and then increase the size to 3-in. diameter.
This rule of thumb applies to inlet pipes that are made of vacuum-rated industrial suction hose and pipe materials including PVC, Schedule 40-80, and black pipe. For exhaust plumbing, this applies to a metal pipe or high-temperature rated hose, which is necessary due to the heat generated within the pump.
ADDITIONAL FRICTION DUE TO BENDS AND FITTINGS
Beyond just the friction of the pipe, pressure loss is increased by turbulence from any changes in direction as well as expansion or contraction due to fittings. These are considered “minor” losses, but they do add up throughout the system. Though a formula exists for calculating these minor losses, they can be estimated as follows.
EQUIVALENT PIPE LENGTHS
Use the following chart to convert each bend to the equivalent pressure loss caused by a straight length of pipe. Then add the equivalent length of all fittings and bends to the nominal length of the pipe to estimate the pressure drop over the total equivalent length of the plumbing system. Note that these equivalent pipe lengths are for pipes made of steel or other common materials according to standard schedules.
EQUIVALENT PIPE LENGTHS FOR 90° ELBOWS
2” diameter pipe
- Long radius elbow: Add approx. 30 in. (760 mm)
- Short radius elbow: Add approx. 60 in. (1520 mm)
3” diameter pipe
- Long radius elbow: Add approx. 40 in. (1015 mm)
- Short radius elbow: Add approx. 80 in. (2030 mm)
4” diameter pipe
- Long radius elbow: Add approx. 50 in. (1270 mm)
- Short radius elbow: Add approx. 100 in. (2540 mm)
For more Rules of Thumb for designing vacuum pump systems, Becker has published a comprehensive Industrial Vacuum Pump Technical Guide for distributors and customers.
BECKER: YOUR VACUUM PUMP EXPERTS
A global leading manufacturer of vacuum equipment, Becker is known for high-quality pumps and expert customer service. Our technical team is available to help you design the most efficient piping system for your application.
For help with vacuum pump pipe sizing, call Becker Pumps’ Technical Support team for assistance.
