- All
- Product Name
- Product Keyword
- Product Model
- Product Summary
- Product Description
- Multi Field Search
Language
Views: 222 Author: Ella Publish Time: 2025-04-17 Origin: Site
Content Menu
● Introduction to Hydraulic Motors and Pumps
>> Torque and Speed Relationship
● What Does "Underrated Pump" Mean?
● The Relationship Between Pump and Motor
● Effects of Using an Underrated Pump
>> 2. Torque Output Remains (If Pressure Is Adequate)
>> 5. System Efficiency and Heat
● Real-World Scenarios and Performance
>> Scenario 1: Wheel Motor with Underrated Pump
>> Scenario 2: Core Drill Motor
● Sizing and Selection Best Practices
>> Why Accurate Sizing Matters
>> Hydraulic Pump and Motor Comparison
● FAQ: Top 5 Questions About Hydraulic Motors and Underrated Pumps
>> 1. Will a hydraulic motor be damaged by an underrated pump?
>> 2. Can I increase the speed of my hydraulic motor with the same pump?
>> 3. What happens if the pump can't supply enough pressure?
>> 4. Is it better to oversize or undersize a hydraulic pump?
>> 5. How do I calculate the required pump size for my hydraulic motor?
Hydraulic systems are the backbone of countless industries, powering everything from construction equipment to manufacturing lines. At the heart of these systems are hydraulic motors and pumps, working in tandem to convert fluid power into mechanical work. But what happens when the pump is "underrated"—that is, when it cannot supply the maximum flow or pressure the motor is designed for? Will the hydraulic motor still function, and if so, what are the consequences? This comprehensive guide explores the science, practical considerations, and real-world outcomes of pairing a hydraulic motor with an underrated pump.
Hydraulic systems use pressurized fluid to transmit power. The hydraulic pump converts mechanical energy (from an engine or electric motor) into hydraulic energy by moving fluid through the system. The hydraulic motor does the reverse: it takes hydraulic energy and converts it back into mechanical energy, producing rotary motion and torque.
- Hydraulic Pump: Generates flow and pressure.
- Hydraulic Motor: Consumes flow and pressure to produce motion.
- Reservoir, valves, hoses, and other components complete the system.
Hydraulic motors are rotary actuators that transform the pressure and flow of hydraulic fluid into rotational force and speed. They come in several types, including gear, vane, and piston motors, each with unique characteristics and applications[3][4].
Basic Operation:
- Pressure determines the torque (rotational force) the motor can produce.
- Flow rate (measured in gallons per minute, GPM, or liters per minute, LPM) determines the speed (RPM) at which the motor shaft turns[3].
- Torque increases with higher pressure.
- Speed increases with higher flow rate.
- "If flow through the motor increases, then the veins will turn faster and the speed of the shaft will increase... increasing the pressure will increase the torque..."[3]
An underrated pump is one that cannot supply the maximum flow or pressure that the hydraulic motor is designed to handle.
- Underrated Flow: Pump delivers less flow (GPM) than the motor's maximum requirement.
- Underrated Pressure: Pump delivers less pressure (PSI) than the motor's maximum rating.
This situation can arise due to design constraints, cost-saving measures, or retrofitting older equipment with newer motors.
The speed of a hydraulic motor is directly proportional to the flow it receives:
Motor Speed (RPM)=[Flow Rate (GPM)×231]/Motor Displacement (in3/rev)
- Lower flow = lower speed
- Higher flow = higher speed
The torque produced by a hydraulic motor depends on the pressure:
Torque (in-lb)=[Pressure (PSI)×Motor Displacement (in3/rev)]/6.28
- Lower pressure = lower torque
- Higher pressure = higher torque
If the pump cannot supply the motor's required flow, the motor will run slower than its rated speed. For example, a 20 GPM motor supplied by a 12 GPM pump will operate at 60% of its maximum speed[1][5].
If the pump can still provide the required pressure, the motor will deliver its rated torque, just at a lower speed[5]. This is because torque is a function of pressure, not flow.
Hydraulic power is the product of pressure and flow. With reduced flow, even if torque is maintained, the overall power output (HP or kW) will be lower.
Hydraulic Power (HP)=[Pressure (PSI)×Flow (GPM)]/1714
If the pump cannot provide enough pressure for the load, the motor may stall or fail to start under heavy load conditions[8].
Running a motor at lower-than-rated flow may reduce system efficiency and generate excess heat, especially if the system is not designed for partial load operation.
- Motor: 20 GPM maximum
- Pump: 12 GPM
Outcome: The motor will work but at a lower speed. Maximum torque can still be achieved if the pump delivers adequate pressure[1].
- Motor requires: 10 GPM at 2000 PSI
- Available pump: 8 GPM at 2100 PSI
Outcome: The motor will spin at 80% of rated speed but can still deliver rated torque. For many applications, this is acceptable if slower operation is not an issue[5].
Selecting the right pump and motor combination is critical for:
- Performance optimization: Ensures machinery operates at peak efficiency.
- Energy savings: Prevents wasted energy and excess heat.
- Longevity: Reduces wear and premature failure[4].
- Load requirements: Calculate torque and speed needed.
- Operating pressure: Ensure the pump can reach the required pressure.
- Flow rate: Match the pump's output to the motor's demand for desired speed.
- Duty cycle: Consider continuous vs. intermittent operation.
- System efficiency: High-efficiency motors and pumps reduce energy costs[4].
- This video explains the principles of hydraulic motor operation, including the relationship between flow, pressure, torque, and speed.
- Demonstrates how changing pump and motor sizes affects speed and torque, with practical examples.
- Shows a hands-on build of a hydraulic kit, illustrating real-world pump and motor interactions.
Will a hydraulic motor still work with an underrated pump? The answer is generally yes, but with important caveats. The motor will operate at reduced speed proportional to the available flow, while torque output can remain unchanged if the pump provides sufficient pressure. However, overall system power will be lower, and in some cases, efficiency may suffer or the motor may stall under heavy loads.
For most applications, running a hydraulic motor with an underrated pump is acceptable if slower operation is not a problem and the load does not exceed the pump's pressure capability. However, for optimal performance, efficiency, and equipment longevity, it is always best to properly size both pump and motor to match the application's demands.
No, as long as the pump does not exceed the motor's pressure rating and the system is properly designed, running a motor at lower flow will not damage it. However, running at low efficiency or frequent stalling can increase wear over time[1][5].
No, speed is determined by flow. To increase speed, you need a pump with a higher flow rate or a motor with smaller displacement[10].
If the pump cannot reach the required pressure for the load, the motor will not develop enough torque and may stall or fail to start under load[8].
Neither is ideal. Oversizing wastes energy and generates heat; undersizing limits performance. Accurate sizing based on load, speed, and duty cycle is best for efficiency and system longevity[4].
Calculate the required flow for desired speed and the required pressure for desired torque. Use the formulas:
Flow (GPM)=[Motor Speed (RPM)×Motor Displacement (in3/rev)]/231
Pressure (PSI)=[Torque (in-lb)×6.28]/Motor Displacement (in3/rev)
[1] https://www.tractorbynet.com/forums/threads/hydraulic-motors-w-undersized-pump.281376/
[2] https://www.istockphoto.com/photos/hydraulic-motor
[3] https://www.youtube.com/watch?v=7aZghp-iI3g
[4] https://www.pooccahydraulic.com/news/how-to-size-a-hydraulic-motor/
[5] https://talk.newagtalk.com/forums/thread-view.asp?tid=286052&DisplayType=nested&setCookie=1
[6] https://hydraulic-motors.org/hydraulic-motors-gallery/
[7] https://www.youtube.com/watch?v=IHXg4dk7Npk
[8] https://bbs.homeshopmachinist.net/forum/general/61761-underpowered-hydraulics-what-happens
[9] https://hydraulic-pumps.org/hydraulic-pumps-gallery/
[10] https://www.youtube.com/watch?v=xo9ws1fslIA
[11] https://mentoredengineer.com/can-a-hydraulic-motor-be-used-as-a-pump/
[12] https://www.tractorbynet.com/forums/threads/hydraulic-motor-and-pump-help.372314/page-2
[13] https://mac-hyd.com/2020/10/19/which-hydraulic-pump-is-right-for-your-needs-2/
[14] https://www.shutterstock.com/search/hydraulic-motor
[15] https://stock.adobe.com/search?k=hydraulic+pump
[16] https://www.topspeed.com/bargain-v12-luxury-coupe-supercar-performance/
[17] https://www.youtube.com/watch?v=buXKmpRZZVc
[18] https://ultimatemotorcycling.com/2025/04/11/2025-triumph-tiger-sport-800-review-14-fast-facts/
[19] https://www.youtube.com/watch?v=5M42kdA5nyU
[20] https://www.shutterstock.com/search/motor-hydraulic
[21] https://www.youtube.com/watch?v=T5scf35GzZM
[22] https://www.reddit.com/r/videos/comments/o21ynj/ram_pumps_move_water_against_gravity_without/
[23] https://www.youtube.com/watch?v=uf-fgSTVnvo
[24] https://www.youtube.com/watch?v=PbI0OX1PkSE
[25] https://www.youtube.com/watch?v=oNl_LUeA2O8
[26] https://www.youtube.com/watch?v=LyrPr-FyDlM
[27] https://www.youtube.com/watch?v=0YiOd2HeS2w
[28] https://www.youtube.com/watch?v=puOUj2XKMOo
[29] https://www.youtube.com/watch?v=v5-wpKW05DA
[30] https://www.youtube.com/watch?v=rBxdGSwB24I
[31] https://www.youtube.com/watch?v=4A5nObh-LlE
[32] https://www.youtube.com/watch?v=DfRuX-TJRaM
[33] https://www.youtube.com/watch?v=qYclytJu4mo
[34] https://www.youtube.com/watch?v=YrpvHS22IO8
[35] https://www.reddit.com/r/Hydraulics/comments/1f3g16l/questions_about_hydraulic_motors/
[36] https://www.hydparts.com/blog/114/faqs-let-s-talk-about-hydraulic-pumps
[37] https://www.linkedin.com/pulse/common-faqs-hydraulic-pumps-hytorc-virginia-axtjc
[38] https://www.whitehouseproductsltd.com/blog/hydraulic-pumps-and-motors-over-pressurization-effects
[39] https://hydraulicpowersales.com/2023/03/how-to-select-the-right-hydraulic-motor/
[40] https://bezares.com/differences-between-hydraulic-pumps-and-hydraulic-motors-a-bezares-product-guide/
[41] https://dynamichydro.co.uk/blog/hydraulic-systems-7-common-problems-with-hydraulic-systems-and-their-solutions/
[42] https://www.hqihydraulics.com/technical-information
[43] https://www.youtube.com/watch?v=82WQTHB0P0c
[44] https://engineering.stackexchange.com/questions/481/motor-for-a-hydraulic-pump-in-a-hydraulic-system
[45] https://www.parker.com/us/en/divisions/hydraulic-pump-and-power-systems-division/solutions/selecting-the-right-motor.html
[46] https://www.reddit.com/r/AskEngineers/comments/3o3x7z/why_would_connect_an_electric_motor_to_a/
[47] https://www.powermotiontech.com/hydraulics/hydraulic-pumps-motors/article/21122383/hydraulic-power-units
[48] https://www.istockphoto.com/photos/hydraulic-pump
[49] https://hydraulic-motors.org/gallery/
[50] https://www.youtube.com/watch?v=sTrEGXXSLSA
[51] https://www.pumps.org/resources/pump-faqs/
[52] https://yorkpmh.com/resources/common-hydraulic-system-problems/
[53] https://orionmotortech.com/blogs/auto-blog/how-to-choose-the-right-hydraulic-pump-size
[54] https://maintenanceworld.com/2013/06/28/a-guide-to-matching-electric-motors-with-hydraulic-power-units/
