Non-Overloading Pumps

How Overloading Affects Motor Life Expectancy

All Irrigation Craft pumps are non-overloading, meaning that the pump impeller cannot load the motor into the motor's service factor at any point on the pump curve.

Why does Irrigation Craft only provide pumps as Non-Overloading?

    Pump motors are often built with Class F insulation systems.  The graph and chart above show the relationship of winding temperature to winding insulation life.  Look on the chart and the graph and you will notice that motor windings with insulation class F working at 155^o C will last 20,000 hours.  (See note below on winding temperature).

20,000 hours is 2.3 years of continuous running 24 hours per day 365 days per year.

 Now, observe the following from the graph:

1.  At 165⁰ C (329⁰ F), a 10^o C (50⁰ F) increase above 155^o C (311⁰ F), winding life decreases by 50% !!!

(20,000 hours versus 10,000 hours).

 

 

 

 

 

 

 

 

 

 

 

 

 

2. At 145^o C (293⁰ F), a 10^o C (50⁰ F) decrease below 155^o C (311⁰ F), winding life increases by 50% !!!

(20,000 hours versus 30,000 hours).

     Temperature has a dramatic effect !!!  Any effort to keep motors cool benefits the owner.  That is why Irrigation Craft spends so much time and effort on this issue.  This is why Irrigation Craft pumps are non-overloading, and this is why Irrigation Craft provides a squirrel cage blower on every enclosed pump station to help cool the motor.  Engineers and designers tell us that when our competition is asked about a cooling fan the typical response is that they have never had a problem that would indicate a cooling fan is needed.

Winding Core Temperature

    The temperature referred to in this document is not the surface of the motor that you can touch, or even the outside or visible part of the windings, but rather, the IMPLIED inside core temperature of the windings.  The surface of a motor is usually much cooler than the core temperature of the windings.  The core temperature is not measured directly, but rather, the temperature is mathematically derived from winding resistance using a standardized test method (NEMA MG1).

Motor Case Surface Temperature

    People often claim a motor is overheating because they feel the motor case and it seems extremely hot, and sometimes paint on the motor case appears discolored and seems burnt.  There may be a problem, but most of the time this complaint is incorrect because motors operating at correct temperatures are often too hot to touch comfortably, and yet nothing is wrong.  Paint applied to the motor case can also be discolored and look burnt and yet nothing is wrong.

    If you feel that a motor is overheating turn the pump off and ask an expert to check it for you.

Follow this link to find an Irrigation Craft Dealer

National Electrical Manufacturer's Association

NEMA MG1 SECTION 9.15.1

    The NEMA motor standard MG1 Section 9.15.1 states that motors have a shortened life span when operated continuously at current levels above FLA but within the service factor.

In Depth Analyses of Overload Situations

    Because most manufacturers use overloading pumps, when there is a system problem causing high flow (and the resulting low pressure), the pump may be loaded beyond its rated horsepower by the impeller.  Here is the sequence of events leading to damage (This is a lengthy sequence of events, see if you can follow to the end).

1. First, an overloading pump & motor combination is used.
2. Second, the overload adjustment is turned up so that the overloading pump can run without nuisance tripping.
3. Third, when a system problem causes high flow the motor heats up.  (Valve stuck on, valve bled on, broken mainline, etc.)
4. Fourth, if the overload protector works the station may turn off on Overload, or the Low Pressure feature may work faster and turn the station off.  This situation becomes a race, the feature (Overload or Low Pressure) with the shortest time delay wins.
5. If the overload protector does not work accurately the motor windings will be overheated and the motor may even burn out.  If the leak is large enough, and if the station has a low pressure feature, and if that feature is working properly, and if that feature is adjusted properly, then the motor may be saved by the low pressure feature.
6. Many manufacturers provide control valves with a Pressure Sustain Feature, claiming that the Sustain feature will protect the motor from overload.  For any application where the Sustain feature was used with a flat curve pump (very common), this feature is typically not useful and often will be found to have been de-adjusted so as to not cause nuisance problems.  Sustain valves cannot reliably sense motor load by pressure when used on flat curve pumps.  Pumps with flat curves should not be equipped with Pressure Sustain valves because the valves result in hyper-sensitive adjustments, unstable adjustments, interfere with normal pump station operating, and cause serious negative consequences to the owner in the form of frequent shut-downs, and in repair costs caused by multiple and frequent service calls.  Many pressure sustain valves will be found to have been de-adjusted because they were a nuisance and interfered with correct pump operation.

 

    With a Non-Overloading pump, if the station has a Low Pressure feature, then the feature can work properly.  If the system develops a high flow demand then the pump will be turned off by the Low Pressure feature instead of by the Overload protection, which is the correct alarm.  Also, if the low pressure feature is not working properly or is maladjusted, the motor will not be damaged because the pump cannot overload the motor no matter high the flow is.

Causes of Motor Over-Heating

Power Supply Problems That Cause Motor Over-Heating

1. Low Voltage - For inductive motors, current (and therefore heat) increase as voltage drops.  Therefore, low voltage can cause high winding temperatures.  Low Voltage can result from power vendor problems such as: transformers are too small, power feed wire too small, poor connections, loose connections, faulty power vendor fuse blades.  Transformers can often be adjusted to provide higher or lower voltages by the power vendor.
2. Unbalanced Power - Unbalanced voltage or current causes increased rotor slippage and erratic slippage, which then causes additional heating of the motor windings.  Unbalanced power can be caused by unbalanced loading of the transformers, loose or poor connections, failed circuit breakers or fuse holders, failed contactors, power vendor problems such as uneven grid loads or site loads.
3. Open Delta Power Systems - Open Delta transformer systems are also commonly referred to as "High Leg" systems because when the three phases are compared to ground or neutral, two of the three phases measure 110/120 volts, while one phase measures 220 volts (the high leg) to ground or neutral.  These systems are inherently unbalanced and inductive loads cannot ever obtain balanced power from these systems.  Some power vendors (Florida Power and Light for example), have internal company policies that they will not supply 3 phase motors larger than 10hp with Open Delta transformers.  Unless special engineering is done with the pump and motor, unbalanced power from Open Delta three phase systems causes shorter motor life, poor pump performance, and also other components on the same transformer may have problems.

 

Motor Problems That Cause Motor Over-Heating

1. Use of Motor Service Factor -  Pumps can be configured to use the motor service factor, and this is in fact quite common.  For constant speed systems it may be advisable to trim the impeller or size the motor so that the pump impeller cannot load the motor into the service factor at any point on the pump curve.
2. Internal Motor Problems - Loose motor connections in the motor junction box, clogged vents, broken fan or fan blades, failed bearings, and a multitude of hard to detect problems in rotors, windings, and stacks.

 

Environmental Causes That Cause Motor Over-Heating

1. High Ambient Temperature Problems  - Excessively high ambient air temperatures are caused by caused by crowded equipment rooms, insufficiently vented or cooled equipment rooms, other equipment close by that is overheating.
2. High Ambient Temperatures Caused By Location - When pump equipment is located in such a place that numerous factors add up to abnormally high temperatures.  An example would be as follows:  A pump station installed on a concrete pad, in a corner of an outside wall, with a southern exposure, with little air circulation.  The two walls reflect radiant heat onto the pump station, the concrete pad reflects radiant heat onto the pump station, the pump station receives radiant heat directly from the sun, the pump station itself, the concrete pad,  and the walls heat the surrounding air, and then combined with little or no air circulation.  So not only is the air temperature 20 degrees higher than surrounding areas, but radiant energy from the walls and the pump station itself  adds even more to the total heat load on the equipment so that that the pump equipment is 40 degrees hotter than other equipment located near by.  If pump station were installed just 10 feet away equipment temperature could drop by 40 degrees.
3. Room Ventilation Problems such as clogged vents or filters, room ventilation fan or air conditioners.

 

System Problems That Cause Motor Over-Heating

1. Frequent Starting - system leaks, no jockey pump or incorrectly chosen jockey pump, incorrect adjustments, poor control system.  Pressure On - Pressure Off control systems are particularly guilty of causing frequent starting and stopping of pumps.  A more robust and correct control system usually monitors flow rate to retire pumps instead of pressure.
2. System Valves "sticking" open.
3. System Valve Overlap.
4. Controller overlap.
5. High Flow Rates Within Zones - Damaged system components such as spray heads, leaks, maladjusted equipment, modified equipment or equipment added that increases flow rates, and nozzle wear (see next item).
6. Nozzle Wear  - Any system with spray nozzles typically uses more water as nozzles age due to wear, and this is especially a problem on systems with any abrasive content such as sand.
7. Incorrect System Design - A common problem caused by carelessness or unknowledgeable system designers.
8. System Installation - Another common problem where systems are not installed per plans and specifications.
9. System Modification - Common problem caused by carelessness, excessive system revisions, or modifications by unqualified persons.
10. Incorrect Pump Selection - Another common problem caused by carelessness, excessive revisions, or incompetence.
11. Marginal Design or Installation - Possibly the most common problem of all.  Marginal systems are defined by edgy or borderline specifications where many small errors add up to cause large problems with no definable single cause.  For instance, an irrigation system design either specified or allows an overloading pump, flow rates are slightly higher than anticipated, wire size feeding the pump is too small, the power source is an open delta system, irrigation heads are spaced too far apart, and finally a few heads are added to fix dry areas.  One of those problems may or may not cause severe problems, but the total effect of all those "little" errors could be catastrophic.

How does Irrigation Craft handle motor heating?

1. Non-Overloading pump and motor combinations.  Impellers are trimmed and motors sized such that the pump is incapable of overloading the motor at any point on the pump curve.

2. Overload modules are set exactly at motor FLA (Full Load Amps).  (When others provide overloading pumps then the motor overload protectors are often adjusted at FLA plus 15% to account for the overloading nature of the pumps, thus making their overload protection less protective and more vulnerable to inaccurate overloads or overload adjustments).  This means that the Irrigation Craft overload feature will be more likely to prevent damage to the motor when there is a serious problem.

3. All enclosed stations are cooled by a squirrel cage blower.  Our competitors frequently use only passive venting (no fan).  Learn more about cooling the enclosure here.

4. On pressure boost systems maintaining a constant high static head, a heat purge system is provided as standard equipment.  Although some manufacturers provide this feature, many do not.  On systems allowed to operate "hot", that is, the pump and fluid inside the pump is allowed to run hot, that heat travels down the motor shaft into the motor, adding to the heat developed in the motor, which may shorten life expectancy of the motor, and in some cases failure occurs quickly.

5. Irrigation Craft pioneered the use of Volute Heat Sensors on pump stations to provide a back up or redundant safety in case other controls failed.  We observed that large and expensive pump stations would burn out motors if a station feature malfunctioned, or if a control adjustment was incorrect.  So Irrigation Craft provides this volute heat sensor as standard equipment on ALL pump stations.  Furthermore, Irrigation Craft has refined our volute heat sensors over the years so that it is easily tested on site in just a few minutes, never causes nuisance alarms, cannot be activated by the sun, and we also test our sensors 100% before installing them.

Related Articles on This Website:

Glossary - Overload

Glossary - Service Factor (SF)

Glossary - Full Load Amps (FLA)

See 2 Pump Graphs - Non-Overloading & Overloading

Learn How to Diagnose OVERLOAD problems

 

 

 

Specifications, Pricing, and all other information on this website are subject to change without notice.