What is pump affinity laws?

The affinity laws (Also known as the Fan Laws or Pump Laws) for pumps/fans are used in hydraulics, hydronics and/or HVAC to express the relationship between variables involved in pump or fan performance (such as head, volumetric flow rate, shaft speed) and power. They apply to pumps, fans, and hydraulic turbines.

How do you use affinity laws?

In other words, if shaft speed increases by 10% then flow at the same head will also increase by 10%. This law is expressed with the following formula: Q₁/Q₂ = (N₁/N₂) or (D₁/D₂) Where Q is equal to flow, N is equal to shaft speed, and D is equal to impeller diameter.

Do affinity laws apply to compressors?

If the compressor flow, head and efficiency characteristics are known at a given speed, then merely applying the affinity laws at an alternate speed will produce a new curve representing the compressor performance at that speed. This is the same concept behind head and flow coefficients.

What pumps similar?

Two pumps are geometrically similar when all corresponding dimensions have the same constant ratio and all angles such as blade angles, β1 and β2 , are equal. Two geometrically similar pumps belong to the same family and are from the same class.

What are the affinity laws by what percent the head will reduce if the pump’s impeller is trimmed by 10%?

If you are trimming impellers on a 10 stage pump, you will need to reduce the amount of trim by roughly 15% to avoid reducing the capacity and head below what you would originally expect from the affinity laws.

What is pump curve?

Pump curves are essentially data about a given pump’s ability to produce flow against certain head. When you’re reading a curve, the pump’s flow rate will be on the top and bottom and its height to push is on the sides.

What is performance curve of a pump?

A pump performance curve indicates how a pump will perform in regards to pressure head and flow. A curve is defined for a specific operating speed (rpm) and a specific inlet/outlet diameter. … The curve also shows the shut off head or the head that the pump would generate if operating against a closed valve.

Does NPSH vary with pump speed?

NPSH-Required increases by the 4/3 power of the pump speed, for a given flow rate and Suction Specific Speed, so assuming that the value of the system NPSH-Available is fixed, lower pump speed can increase the NPSH-Margin, and therefore, pump reliability.

What does an impeller do?

WHAT DO IMPELLERS DO? Impellers pump cold water into your boat’s engine to cool it down while in use. If you have a bad impeller it can cause big problems.

Which law is used in electric fan?

Faraday’s Law Faraday’s Law says that if you want the motor to spin faster, just turn up the voltage. If you picture an electric fan, the higher the voltage applied, the faster the motor works, and the faster the blades turn.

How do you read a centrifugal pump curve?

What is the fan law?

The Fan Laws are a group of useful equations for determining the effects of a change in the speed, the diameter of the fan and the density of air in the system. They are most useful for determining the impact of extrapolating from a known fan performance to a desired performance.

What are three different types of water pumps?

There are three basic types of pumps: positive-displacement, centrifugal and axial-flow pumps.

What are the 3 types of centrifugal pumps?

Single-stage, Two-stage, or Multi-stage.

What is the most efficient pump type?

centrifugal pumps Positive displacement pumps are able to handle variations in pressure, flow and viscosity and remain efficient, unlike centrifugal pumps which do not operate well off the centre of their curve.

What happens when you trim an impeller?

Trimming involves machining the impeller to reduce its diameter. … As the impeller diameter decreases, added clearance between the impeller and the fixed pump casing increases internal flow recirculation, causes head loss, and lowers pumping efficiency.

What is the effect of trimming of impeller?

Trimming the impeller results in a change in the length and outlet angle of the vane as well as the width of the impeller at the outlet. The effect of this measure thus depends on the type of impeller. Single-vane and diagonal impellers can only be trimmed within narrow limits.

Why pumps are generally less efficient than turbines?

The pump is inherently less efficient than a turbine because of smaller losses when converting pressure energy to kinetic energy than vice versa.

What is performance curve?

A performance curve, also known as a bell curve, is a systematic measure for assessing employees’ performance via a graphic diagram.

What is NPSH pump curve?

The NPSH curve displays the minimum required inlet pressure (expressed in m) allowing the pump to pump in accordance with the performance curve and in order to prevent evaporation of the pumped fluid so as to avoid cavitation inside the pump.

What is the difference between system curve and pump curve?

In general, a pump is used to overcome frictional head loss in piping systems as well as system elevation changes between system boundaries (i.e., static head). … The system curve helps quantify the resistance in a system due to friction and elevation change over the range of flows.

What happens when a pump runs off its curve?

If a pump is running out on the end of the curve it can cause cavitation inside the pump and result in premature wear of the impeller and bearings of the motor. It can also cause the motor to over amp and prematurely fail.

How does a VFD affect a pump curve?

Most often, only a pump curve at a single fixed speed is available. … A VFD can help here by raising the pump’s operating speed to a higher-than-standard rpm so the pump curve and system curve intersect at the desired flow rate — but at the expense of higher power requirements.

How do you plot a pump performance curve?

What happens if NPSH is less than Npshr?

When the pump is running, the reading from this gauge will be equal to your NPSHA, less vapor pressure. If after subtracting vapor pressure this value is less than the pump’s NPSHR, you have confirmed that this is a cavitation problem.

What is the effect of NPSH on cavitation?

NPSH is particularly relevant inside centrifugal pumps and turbines, which are parts of a hydraulic system that are most vulnerable to cavitation. If cavitation occurs, the drag coefficient of the impeller vanes will increase drastically—possibly stopping flow altogether—and prolonged exposure will damage the impeller.

What happens if NPSH is negative?

The NPSH is supplied from the system and is solely a function of the system design on the suction side of the pump. … If the liquid is below the pump, this becomes a negative value. Hvp = The vapour pressure of the liquid at the pumping temperature expressed in feet of head.

Which type of impeller is most efficient?

1. Zinc was observed to be the most efficient impeller material with greater pump head and flow rate than the cast iron impeller and the bronze impeller.

How often should an impeller be replaced?

How often should the impeller on a boat be replaced? It is recommended that a boat impeller be replaced every two to three years or 300 hours, whichever comes first. However, it is suggested to also visually inspect your impeller at the beginning of each season for any signs of wear or damage.

Should you grease an impeller?

When inserting an impeller, be sure to use durable water proof grease or other lubricating agent suitable for the purpose and approved by the pump manufacturer on the shaft, so that the impellor will be less likely to become seized to the shaft over time and will be more readily removable when the time comes to do so.