Selecting the Proper Water Pump

Introduction

Choosing the right irrigation pump is one of the most important decisions when designing an irrigation system. An undersized pump can result in poor pressure, inadequate coverage, and unhappy customers. An oversized pump can waste energy, increase operating costs, and shorten equipment life.

Proper irrigation water pump sizing ensures your system delivers the flow and pressure needed to keep landscapes, agricultural operations, nurseries, golf courses, and commercial properties operating efficiently.

In this guide, we'll explain the key factors involved in sizing an irrigation pump and help you determine which Goulds pump may be the best fit for your application.

---

Understanding the Three Key Pump Sizing Factors

Before selecting a pump, you need to understand three critical measurements:

Flow Rate (GPM)

Flow rate is measured in gallons per minute (GPM) and represents how much water your irrigation system requires while it is operating.

To calculate flow requirements:

• Determine the GPM demand of each irrigation zone.
• Identify which zones will operate simultaneously.
• Size the pump based on the highest flow demand that will occur at one time.

For example:

• Zone 1 = 12 GPM
• Zone 2 = 8 GPM
• Zone 3 = 15 GPM

If your irrigation controller is programmed to run one zone at a time, the pump only needs to support the largest zone demand—in this case, 15 GPM.

However, if Zones 1 and 2 are designed to operate simultaneously, the pump would need to deliver 20 GPM.

Most residential and commercial irrigation systems are divided into zones specifically to avoid exceeding the available water supply or pump capacity. When sizing a pump, focus on the maximum flow demand that will occur at any given time rather than simply adding every zone together.

Total Dynamic Head (TDH)

Total Dynamic Head measures the total resistance the pump must overcome.

TDH includes:

• Vertical lift

• Friction loss in piping

• Pressure requirements at the irrigation heads

• Elevation changes

The higher the TDH, the harder the pump must work.

Pressure Requirements

Most irrigation systems require between:

• 30-60 PSI for residential systems

• 40-80 PSI for commercial irrigation

• Higher pressures for specialized agricultural applications

Always verify the pressure requirements of your sprinklers, drip systems, or irrigation equipment before selecting a pump.

---

How to Calculate Irrigation Pump Size

Step 1: Determine Your Water Source

The source of your water affects pump selection.

Common sources include:

• Shallow wells

• Deep wells

• Ponds

• Lakes

• Retention ponds

• Municipal water storage tanks

Each source creates different lift and suction requirements.

Step 2: Calculate Required GPM

Calculate the flow requirement for the largest zone or combination of zones that will operate simultaneously.

In most irrigation systems, zones are intentionally designed to run one at a time because the available water supply or pump capacity cannot support every zone operating together.

Example:

• Zone 1 contains four rotors at 4 GPM each
• Total Zone Demand = 16 GPM

If only one zone operates at a time, the pump must be capable of supplying at least 16 GPM, plus a reasonable margin for efficiency and future expansion.

If multiple zones are intended to run simultaneously, add their flow requirements together and size the pump accordingly.

Understanding how your irrigation controller is programmed is critical when sizing a pump. Oversizing or undersizing often occurs when total property demand is confused with actual operating demand.

Step 3: Calculate Total Dynamic Head

Add:

• Suction lift

• Pipe friction loss

• Elevation gain

• Required discharge pressure

Example:

Factor	Feet
Suction Lift	10
Friction Loss	15
Elevation Gain	5
Required Pressure (40 PSI)	92
Total Dynamic Head	122

This information allows you to compare your requirements against pump performance curves.

---

Common Irrigation Pump Sizing Mistakes

Choosing Based on Horsepower Alone

Many buyers assume more horsepower automatically means better performance.

In reality, horsepower is only one factor.

A properly sized 1 HP pump can outperform an improperly selected 2 HP pump when matched correctly to the application.

Ignoring Friction Loss

Long pipe runs can significantly reduce system performance.

Contractors should always account for:

• Pipe diameter

• Pipe length

• Number of fittings

• Valves and accessories

Failing to Plan for Expansion

Future irrigation zones often increase demand.

If expansion is likely, selecting a pump with additional capacity can prevent costly upgrades later.

---

Choosing the Right Goulds Pump for Your Irrigation System

Goulds Water Technology pumps are widely recognized throughout the irrigation industry for their durability, efficiency, and long service life. ASIW Supply carries several popular Goulds models that serve a variety of irrigation applications.

Goulds J5S for Small Irrigation Systems

The Goulds J5S is ideal for:

• Residential irrigation

• Small agricultural systems

• Garden watering applications

• Shallow well installations

Key specifications include:

• 1/2 HP motor

• Up to 21 GPM flow

• Self-priming design

• Dual-voltage operation (115/230V)

Product Link: Goulds J5S Self-Priming Shallow Well Jet Pump

Goulds J7S for Medium-Duty Irrigation Applications

For properties requiring additional flow and pressure, the Goulds J7S provides:

• 3/4 HP performance

• Up to 22 GPM

• Self-priming operation

• Heavy-duty cast iron construction

This model works well for larger residential properties and small commercial irrigation systems.

Product Link: Goulds J7S Self-Priming Shallow Well Jet Pump

Goulds J10S for Commercial Irrigation Systems

The Goulds J10S is frequently selected for:

• Commercial landscaping

• Greenhouses

• Nurseries

• Municipal irrigation systems

Features include:

• 1 HP motor

• Up to 23 GPM

• Continuous-duty operation

• Thermal overload protection

Product Link: Goulds J10S Self-Priming Shallow Well Jet Pump

Goulds GT15 and GT20 for High-Demand Irrigation Systems

When flow requirements increase, many contractors move to Goulds IRRI-GATOR centrifugal pumps.

These pumps are commonly used for:

• Golf courses

• Large agricultural systems

• Commercial landscapes

• Sports fields

• Municipal irrigation networks

Product Links:

• Goulds GT15 IRRI-GATOR Pump

• Goulds GT20 IRRI-GATOR Pump

The GT20 is one of the most popular choices for larger irrigation systems due to its 2 HP motor and ability to handle demanding water delivery requirements.

---

Frequently Asked Questions

What size pump do I need for a 20 GPM irrigation system?

The correct pump depends on both flow and total dynamic head. A system requiring 20 GPM at higher pressure may require a significantly different pump than a 20 GPM low-pressure system.

Is a larger pump always better?

No. Oversizing can increase energy costs, cause pressure issues, and reduce system efficiency.

How do I know if my irrigation pump is undersized?

Common signs include:

• Low sprinkler pressure

• Uneven coverage

• Pump constantly running

• Poor performance during peak demand

---

Conclusion

Proper irrigation water pump sizing starts with understanding your required flow rate, pressure requirements, and total dynamic head. By accurately calculating these factors, contractors and property owners can select a pump that delivers reliable performance while minimizing operating costs.

Whether you're designing a residential irrigation system or a large-scale agricultural operation, ASIW Supply offers dependable Goulds pumps to match virtually any application. Our team can help evaluate your system requirements and recommend the right pump for long-term performance and reliability.

Need Help Sizing a Pump?

Contact ASIW Supply for expert guidance on Goulds pumps, irrigation systems, PVC pipe, fittings, and fluid transfer products. We proudly serve contractors, municipalities, agricultural operations, and industrial customers throughout Florida and across the United States.