When you need maximum power, durability, and performance, Foster Hydraulics delivers diesel hydraulic power units that are engineered to handle the most demanding conditions. For decades, we’ve been the trusted name in custom-built hydraulic solutions, serving industries nationwide with equipment designed for efficiency, reliability, and long-term performance. Whether your operation is on the Alaska tundra, an oil rig in the Gulf of Mexico, or anywhere in between, our diesel power units are built to keep your work moving.

Our diesel hydraulic power units are built stronger than industry standards—because heavy-duty should mean more than just a label. We use premium diesel engines from John Deere, Kubota, and Kohler, paired with thermostat-controlled heat exchangers, reservoir heaters, and pressure-compensated pumps to ensure smooth operation in even the harshest environments. Every unit can be customized with a range of hydraulic control valves, larger fuel tanks for extended run times, and oversized reservoirs for better heat management and improved system longevity.

The Complete Guide to Diesel Hydraulic Power Units

Diesel hydraulic power units provide independent hydraulic power for equipment operating where electrical service is unavailable, impractical, or unreliable. They are commonly used at construction sites, industrial facilities, marine terminals, utility projects, agricultural operations, forestry sites, mines, oil fields, and other demanding locations.

A properly designed diesel hydraulic power unit is more than an engine connected to a pump. It is a complete hydraulic system in which the engine, pump, reservoir, valves, filtration, cooling equipment, controls, and structural frame must work together.

Foster Hydraulics designs and manufactures custom diesel hydraulic power units for commercial, industrial, mobile, marine, and specialty applications. Available Foster configurations include compact 25 HP systems and larger Kubota- and John Deere-powered units in multiple horsepower ranges.

This guide explains how diesel hydraulic power units work, how their major components are selected, and what buyers should consider when specifying a system.

What Is a Diesel Hydraulic Power Unit?

A diesel hydraulic power unit, sometimes called a diesel HPU, hydraulic power pack, or diesel-driven hydraulic unit, uses a diesel engine to drive a hydraulic pump.

The pump draws hydraulic oil from a reservoir and sends it through a hydraulic circuit. The circuit controls the fluid’s pressure, flow rate, direction, and return path. That hydraulic power can then operate equipment such as:

• Hydraulic cylinders
• Hydraulic motors
• Winches
• Cranes
• Presses
• Boring and drilling equipment
• Construction tools
• Conveyors
• Compactors
• Dock equipment
• Agricultural machinery
• Remote hydraulic circuits

A basic hydraulic circuit normally includes a power source, hydraulic pump, reservoir, relief valve, directional control valve, and hydraulic actuator. Filtration and cooling components help control contamination and operating temperature.

How a Diesel Hydraulic Power Unit Works

The diesel engine converts fuel into mechanical power. A coupling or drive assembly transfers that mechanical power to the hydraulic pump.

The operating sequence is generally:

1. The diesel engine rotates the hydraulic pump.
2. The pump draws oil from the hydraulic reservoir.
3. The pump produces hydraulic flow.
4. Resistance to that flow creates pressure.
5. Control valves direct the oil to the required function.
6. Hydraulic cylinders or motors convert hydraulic energy into mechanical movement.
7. Return oil passes through the circuit and filtration system before returning to the reservoir.
8. A heat exchanger may remove excess heat before the oil reenters the system.

It is important to understand that a hydraulic pump primarily produces flow. Pressure develops when the flow encounters resistance from a load, restriction, actuator, or control device.

System performance therefore depends on both flow and pressure:

• Flow, measured in gallons per minute, primarily determines actuator speed.
• Pressure, measured in pounds per square inch, primarily determines available force or torque.

Both values must be specified when selecting a power unit.

When Should You Use a Diesel Hydraulic Power Unit?

Diesel power is particularly useful when equipment must operate independently of an electrical power source.

A diesel hydraulic unit may be the right choice when:

• Three-phase electrical power is unavailable.
• The equipment must move between job sites.
• The system will operate outdoors.
• High hydraulic horsepower is required.
• Long operating periods are expected.
• The unit must support remote equipment.
• The application requires a self-contained power source.
• A gasoline engine would be undersized for the required duty.
• The job requires greater fuel efficiency under sustained loads.
• The surrounding equipment already uses diesel fuel.

Foster diesel hydraulic power units are designed for demanding environments ranging from cold-weather operations to marine and offshore locations. Available system features include thermostat-controlled heat exchangers, reservoir heaters, pressure-compensated pumps, multiple valve configurations, certified welding, and optional marine-grade powder coating.

Major Components of a Diesel Hydraulic Power Unit

Diesel Engine

The engine must produce enough continuous horsepower to operate the hydraulic pump at the required flow and pressure.

Foster diesel hydraulic units are available with Kubota and John Deere engines. Foster’s diesel product range includes compact systems as well as larger configurations for high-flow and high-duty applications.

Important engine considerations include:

• Rated horsepower
• Continuous-duty capability
• Operating RPM
• Cooling system
• Emissions compliance
• Fuel consumption
• Starting system
• Control panel
• Service accessibility
• Environmental conditions

For example, Foster’s 25 HP diesel unit uses a liquid-cooled Kubota diesel engine with direct fuel injection, electric start, battery and case, and a control panel. The listed design is Final Tier 4 emissions compliant.

Larger Foster units may use turbocharged Kubota engines. The Foster 65K-1-35 D/C unit, for example, uses a 65 HP Kubota V2403T liquid-cooled diesel engine with a diesel oxidation catalyst system and Final Tier 4 certification.

Hydraulic Pump

The hydraulic pump is one of the most important components in the system. It must provide the correct flow at the required operating pressure while staying within the available engine horsepower.

Common pump types include:

Fixed-Displacement Gear Pumps

Gear pumps produce a fixed amount of oil per revolution. They are widely used because they are:

• Economical
• Durable
• Relatively simple
• Well suited for open-center circuits
• Available in multiple displacements

Foster offers heavy-duty American or European gear-pump configurations on its diesel hydraulic systems.

Pressure-Compensated Piston Pumps

A pressure-compensated piston pump automatically reduces displacement when the system reaches its pressure setting and flow demand decreases.

These pumps are commonly selected for:

• Closed-center valve systems
• Variable flow requirements
• Multiple hydraulic functions
• Applications with significant idle time
• Systems where heat reduction is important
• More advanced industrial controls

Foster builds pressure-compensated diesel systems and offers pressure-compensated piston pumps as an alternative to fixed-displacement gear pumps.

Tandem or Multiple Pumps

A tandem-pump arrangement allows one engine to power two or more hydraulic circuits. This can be useful when an application requires:

• Different flow rates
• Independent functions
• Separate pressure ranges
• Simultaneous operation
• A high-flow and low-flow circuit
• Dedicated auxiliary hydraulics

The correct arrangement depends on the required operating sequence and the total horsepower needed when functions operate simultaneously.

Calculating Hydraulic Horsepower

The theoretical hydraulic horsepower requirement is calculated from flow and pressure.

Hydraulic horsepower = GPM × PSI ÷ 1,714

Actual systems experience mechanical and hydraulic losses. Pump efficiency must therefore be included when selecting the engine:

Required horsepower = GPM × PSI ÷ (1,714 × efficiency)

Foster Hydraulics uses this efficiency-adjusted formula in its hydraulic horsepower calculator.

Example: 35 GPM at 3,000 PSI

The theoretical hydraulic horsepower is:

35 × 3,000 ÷ 1,714 = approximately 61.3 HP

Because real equipment is not 100% efficient, the selected engine must be larger than 61.3 HP. The exact requirement depends on pump efficiency, drive losses, engine performance at operating RPM, ambient conditions, and whether the pressure and flow occur continuously.

Foster’s 65 HP 65K-1-35 D/C is rated for 35 GPM at 3,000 PSI working pressure, illustrating the close relationship between engine horsepower, flow, and pressure.

Engine sizing should never be based on pump flow alone. A 35 GPM pump operating at low pressure requires far less horsepower than the same pump operating at 3,000 PSI.

Hydraulic Reservoir Sizing

The hydraulic reservoir stores oil, helps separate air from the fluid, allows contamination to settle, and provides surface area for heat dissipation.

Reservoir selection depends on:

• Pump flow
• Duty cycle
• Operating temperature
• Available cooling
• Cylinder displacement
• Hose and piping volume
• Installation space
• Machine orientation
• Environmental conditions

Foster’s standard 25 HP diesel configuration includes a 25-gallon hydraulic reservoir. Its 65 HP, 35 GPM unit includes a 50-gallon reservoir. Larger reservoir options are available when an application requires increased oil capacity or improved heat management.

A larger reservoir can provide several benefits:

• More oil available for the complete circuit
• Increased dwell time before the fluid returns to the pump
• Better heat dissipation
• Improved air separation
• Greater tolerance for oil-level changes
• Longer operating periods between inspections

However, a larger tank also increases weight, dimensions, oil cost, and required mounting space. Reservoir size should be engineered for the actual application rather than selected only by a general rule of thumb.

Hydraulic Cooling and Heat Exchangers

Heat is generated whenever hydraulic power is lost through inefficiency, pressure drop, leakage, throttling, or continuous relief-valve flow.

Excess heat can:

• Reduce oil viscosity
• Shorten seal life
• Accelerate oil breakdown
• Reduce lubrication
• Damage hydraulic components
• Cause inconsistent operation
• Increase downtime

Foster diesel hydraulic power units can be equipped with thermostat-controlled, fan-cooled heat exchangers. Reservoir heaters are also available for cold-weather environments.

The Foster 25 HP diesel unit includes a fan-cooled heat exchanger with an adjustable thermostat. The 65 HP unit also includes a fan-cooled heat exchanger controlled by an adjustable thermostat.

Cooling-system selection should consider:

• Continuous or intermittent duty
• Total system inefficiency
• Ambient temperature
• Engine heat
• Reservoir size
• Required oil temperature
• Airflow around the unit
• Enclosure design
• Maximum allowable component temperature

A properly sized cooler should be based on estimated heat rejection, not simply pump horsepower.

Filtration and Oil Cleanliness

Clean hydraulic oil is critical to reliable operation. Contamination can damage pumps, valves, seals, and precision hydraulic components.

Common filtration locations include:

• Suction line
• Pressure line
• Return line
• Offline filtration loop
• Reservoir fill connection
• Reservoir breather

Foster’s 25 HP diesel unit includes a 10-micron return-line filter. The 65 HP unit uses a submerged-style 10-micron return filter. Both units include a sight, level, and temperature gauge to assist with oil-level and temperature monitoring.

Foster recommends clean, anti-wear hydraulic oil with rust protection and anti-foaming additives. Its hydraulic oil guidance identifies viscosity, lubricity, thermal stability, low foaming, demulsibility, heat-transfer capability, corrosion resistance, and cleanliness as important fluid properties. Foster also recommends filtering even new oil before use and references 10-micron filtration.

Selecting Hydraulic Oil

Hydraulic oil must remain thick enough to provide lubrication and sealing, but not so thick that it causes excessive pressure drop or poor cold-weather performance.

The correct fluid depends on:

• Ambient temperature
• Normal operating temperature
• Pump requirements
• System pressure
• Seal compatibility
• Environmental exposure
• Fire-resistance requirements
• Manufacturer recommendations

Foster’s standard fluid guidance references an anti-wear ISO Grade 32 hydraulic oil and lists comparable products from several oil manufacturers. Final oil selection should still account for the pump manufacturer’s requirements and the application’s expected temperature range.

Low temperature can make hydraulic oil too thick, causing:

• Difficult starting
• Pump cavitation
• Slow actuator response
• Increased pressure drop
• Filter bypass
• Pump damage

High temperature can make the oil too thin, causing:

• Increased internal leakage
• Reduced lubrication
• Lower system efficiency
• Accelerated seal wear
• Shortened oil life

Cold-weather diesel units may therefore require reservoir heaters, appropriate viscosity selection, and a warm-up procedure.

Hydraulic Control Valves

Control valves determine where oil flows, when an actuator moves, and how the equipment behaves in neutral.

Available control methods include:

• Manual levers
• Mechanical linkages
• 12- or 24-volt DC solenoids
• 120-volt AC solenoids
• Push-button controls
• Foot pedals
• Wired pendants
• Wireless remote controls
• PLC-based controls

Foster designs hydraulic circuits using manual and solenoid-operated valves, including controls compatible with PLC systems.

Open-Center Systems

An open-center valve normally allows pump flow to pass through the valve and return to the reservoir while the valve is in neutral.

Open-center systems are commonly paired with fixed-displacement gear pumps.

Advantages include:

• Simpler design
• Lower initial cost
• Straightforward troubleshooting
• Continuous circulation in neutral

Open-center circuits are often suitable when only one function operates at a time.

Closed-Center Systems

A closed-center valve blocks flow in neutral. It is normally paired with a pressure-compensated variable-displacement pump.

Advantages may include:

• Reduced unnecessary pump flow
• Lower heat generation
• Better efficiency during standby
• Support for multiple functions
• More advanced system control

Foster offers closed-center, pressure-compensated systems for applications requiring this type of performance.

Directional Valve Configurations

Common valve configurations include:

• Three-way, two-position selector valves
• Three-way, three-position valves for single-acting cylinders
• Four-way, three-position valves for double-acting cylinders
• Motor-spool valves
• Float-position valves
• Detented valves
• Monoblock valves
• Sectional valve banks

The neutral spool condition is especially important. A cylinder, hydraulic motor, winch, or conveyor may require a different center configuration.

The standard Foster 25 HP and 65 HP diesel systems include manually operated three-way, two-position selector valves for basic on/off circuit control. Additional valve arrangements are available for more complex applications.

Pressure Control and System Protection

A relief valve protects the circuit from pressure above its setting. It is an essential safety and equipment-protection component, but it should not normally be used as a continuous flow-control device.

Continuous flow across a relief valve creates heat and wastes engine power.

Foster diesel units include adjustable relief valves and liquid-filled pressure gauges. The 25 HP unit includes a 0–3,000 PSI gauge, while the 65 HP model includes a 0–4,000 PSI gauge.

A complete system may also require:

• Port relief valves
• Cross-port relief valves
• Pressure-reducing valves
• Counterbalance valves
• Unloading valves
• Sequence valves
• Thermal relief valves
• Pilot-operated check valves
• Load-holding valves

These devices must be selected according to the load, actuator, operating sequence, and potential failure modes.

Fuel Capacity and Operating Time

Fuel-tank sizing affects how long the unit can operate between refueling stops.

Foster’s 25 HP diesel unit includes a 12-gallon fuel tank and lists fuel use at approximately 2 gallons per hour for the specified configuration. Actual consumption varies with engine load, operating speed, hydraulic demand, ambient conditions, and duty cycle.

The Foster 65 HP unit includes a 25-gallon fuel tank. Larger fuel tanks are available for extended operation.

For applications where downtime is costly, buyers should calculate:

• Expected engine load
• Hours per shift
• Number of shifts
• Refueling access
• Safe fuel capacity
• Required reserve
• Unit weight with a full tank

Extended-run tanks can increase productivity, but they also increase weight and may affect transport requirements.

Skid-Mounted, Portable, and Mobile Configurations

Diesel hydraulic power units may be mounted in several ways.

Skid-Mounted Units

Skid-mounted systems are well suited for:

• Industrial facilities
• Construction sites
• Temporary installations
• Dockside equipment
• Stationary machinery
• Equipment rental fleets

Foster diesel units use heavy-duty skid or platform frames with forklift access. Protective cages and overhead lifting provisions are available on applicable models.

Portable Units

Portable units may include:

• Forklift pockets
• Crane-lifting points
• Compact frames
• Protective cages
• Quick couplers
• Integrated controls

Foster manufactures portable hydraulic power units powered by electric motors, Honda gasoline engines, and Kubota or John Deere diesel engines. Its portable systems can be built as modified basic systems or complete application-specific packages.

Trailer-Mounted Units

A trailer-mounted system may be preferred when the unit must frequently travel between sites.

Trailer design should consider:

• Total operating weight
• Axle and tire capacity
• Tongue weight
• Fuel and oil containment
• Road-lighting requirements
• Equipment tie-down points
• Weather protection
• Hose storage
• Braking requirements
• Service access

Environmental Protection and Enclosures

Operating environment should be defined before the unit is designed.

Important conditions include:

• Outdoor exposure
• Rain and snow
• Saltwater or salt air
• Dust
• Extreme heat
• Freezing temperatures
• Explosive or hazardous areas
• High altitude
• Poor ventilation
• Noise restrictions

Available protective features may include:

• Marine-quality powder coating
• Drip-containment pans
• Protective cages
• Engine and component enclosures
• Reservoir heaters
• Thermostat-controlled cooling
• Weather-resistant controls
• Special filtration
• Stainless-steel components
• Lifting provisions

Foster offers marine-quality powder coating, certified welding, containment options, protective cages, and cooling or heating features for demanding environments.

Common Diesel Hydraulic Power Unit Applications

Foster identifies applications for its diesel units across industrial, construction, utility, forestry, marine, and agricultural operations.

Typical uses include:

Construction

• Hydraulic breakers
• Boring equipment
• Pipe handling
• Jacking systems
• Concrete equipment
• Temporary hydraulic service
• Bridge and structural work

Marine and Dockside

• Winches
• Cranes
• Dock levelers
• Hatch systems
• Barge equipment
• Ship-maintenance tools
• Remote hydraulic systems

Utility Work

• Cable pulling
• Underground installation
• Pipe fusion equipment
• Hydraulic tools
• Temporary emergency power
• Remote valve operation

Forestry

• Log handling
• Splitters
• Conveyors
• Sawmill equipment
• Grapples
• Portable processing equipment

Agriculture

• Augers
• Conveyors
• Irrigation equipment
• Grain-handling equipment
• Remote cylinders and motors
• Replacement power for tractor-driven circuits

Industrial Applications

• Presses
• Material-handling systems
• Compactors
• Test stands
• Production machinery
• Emergency or backup hydraulic power
• Remote plant equipment

Foster Diesel Hydraulic Power Unit Sizes

Foster Hydraulics lists multiple diesel product categories, including:

• 10 HP Kubota diesel units
• 25 HP Kubota diesel units
• Compact 25 HP Kubota units
• 49 HP Kubota units
• 65 HP Kubota units
• 74 HP Kubota units
• 74 HP John Deere units
• 99 HP Kubota units

These categories allow a system to be selected or customized according to required hydraulic horsepower, operating pressure, flow rate, dimensions, mobility, and duty cycle.

Example: Foster 25 HP Diesel Hydraulic Power Unit

The Foster 25 HP line is intended for commercial, industrial, and mobile requirements.

Available standard pump configurations include:

• 10 GPM at 3,000 PSI
• 12 GPM at 2,500 PSI
• 15 GPM at 2,000 PSI

The standard configuration includes a 25 HP Kubota liquid-cooled diesel engine, 25-gallon hydraulic reservoir, 12-gallon fuel tank, adjustable relief valve, pressure gauge, 10-micron return filter, fan-cooled heat exchanger, thermostat, electric start, forklift-accessible skid, and quick couplers.

Example: Foster 65 HP Diesel Hydraulic Power Unit

The Foster 65K-1-35 D/C includes:

• 65 HP Kubota liquid-cooled diesel engine
• Electronic engine control console
• 25-gallon fuel tank
• 35 GPM fixed-displacement gear pump
• 50-gallon hydraulic reservoir
• Adjustable relief valve
• 0–4,000 PSI pressure gauge
• 10-micron return filter
• Thermostat-controlled fan cooler
• Heavy-duty electric starting system
• Forklift-accessible skid

The system is rated for 35 GPM at 3,000 PSI working pressure. Foster also offers larger tank sizes, pressure-compensated piston pumps, protective cages, flow meters, containment pans, and marine-quality coatings.

How to Specify a Diesel Hydraulic Power Unit

Before requesting a quote, gather as much of the following information as possible.

Hydraulic Performance

• Required flow in GPM
• Normal operating pressure
• Maximum pressure
• Continuous or intermittent duty
• Number of hydraulic circuits
• Whether functions operate simultaneously
• Required cylinder speeds
• Hydraulic motor displacement and speed
• Maximum starting load

Circuit Requirements

• Open-center or closed-center circuit
• Gear pump or pressure-compensated piston pump
• Manual or solenoid valves
• Valve spool configurations
• Flow controls
• Load-holding requirements
• Relief-valve settings
• Remote control requirements
• PLC interface requirements

Mechanical Requirements

• Skid, cage, trailer, or enclosed frame
• Maximum dimensions
• Maximum weight
• Forklift access
• Crane-lifting points
• Hose and quick-coupler requirements
• Fuel-tank capacity
• Hydraulic reservoir capacity

Environmental Requirements

• Lowest ambient temperature
• Highest ambient temperature
• Indoor or outdoor installation
• Marine or corrosive exposure
• Dust level
• Altitude
• Noise restrictions
• Containment requirements
• Required finish or coating

Documentation

• Hydraulic schematic
• Electrical schematic
• Component manuals
• Engine documentation
• Dimensional drawing
• Maintenance instructions
• Replacement-parts list
• Testing requirements

Providing complete information early helps prevent an undersized engine, incorrect valve configuration, insufficient cooling, excessive heat, or inadequate reservoir capacity.

Maintenance of a Diesel Hydraulic Power Unit

A preventive-maintenance program should include the diesel engine and the hydraulic system.

Before Each Shift

• Check engine oil.
• Check hydraulic oil level.
• Inspect for leaks.
• Check fuel level.
• Inspect hoses and fittings.
• Verify that guards are secure.
• Inspect the filter indicator, when equipped.
• Check the radiator and heat-exchanger area.
• Confirm that controls operate correctly.

At Regular Service Intervals

• Change engine oil and filters.
• Service fuel filters.
• Inspect belts and hoses.
• Check battery condition.
• Inspect pump coupling.
• Replace hydraulic filter elements.
• Test relief-valve settings.
• Inspect quick couplers.
• Clean the heat exchanger.
• Check hydraulic oil condition.
• Tighten mounting hardware.
• Inspect welds, frame members, and lifting points.

Hydraulic Oil Maintenance

Oil should be checked for:

• Water contamination
• Cloudiness
• Darkening
• Burnt odor
• Foaming
• Visible particles
• Unusual viscosity
• Excessive operating temperature

Foster emphasizes the importance of clean oil and notes that contamination can quickly damage pumps with close internal tolerances.

Common Problems and Troubleshooting

The Engine Stalls Under Hydraulic Load

Possible causes include:

• Engine horsepower is too low.
• Relief pressure is set too high.
• The pump is oversized.
• The load is mechanically jammed.
• The engine is not reaching rated RPM.
• The pump or coupling is damaged.
• Hydraulic oil is too cold and viscous.

The Unit Runs Hot

Possible causes include:

• Continuous relief-valve flow
• Incorrect valve center
• Undersized reservoir
• Undersized heat exchanger
• Dirty cooler
• Restricted return line
• Excessive internal leakage
• Incorrect oil viscosity
• Pump operating continuously at high pressure
• Poor airflow through an enclosure

Hydraulic Functions Move Too Slowly

Possible causes include:

• Pump wear
• Low engine RPM
• Flow-control setting
• Internal cylinder leakage
• Valve leakage
• Incorrect pump displacement
• Restricted suction line
• Low oil level
• Excessive oil viscosity

The Pump Is Noisy

Possible causes include:

• Low oil level
• Suction restriction
• Air entering the suction line
• Oil that is too thick
• Dirty suction strainer
• Excessive pump speed
• Cavitation
• Misaligned coupling
• Worn pump components

Hydraulic Oil Foams

Possible causes include:

• Air leak in the suction line
• Low reservoir level
• Return oil entering above the fluid level
• Incorrect hydraulic oil
• Contaminated oil
• Insufficient reservoir dwell time

Diesel vs. Gasoline Hydraulic Power Units

Diesel units are generally selected for higher horsepower, longer duty cycles, and demanding commercial or industrial work.

A gasoline unit may be preferred when:

• Lower horsepower is sufficient.
• Initial cost is a major consideration.
• The unit is smaller and more portable.
• Operation is intermittent.
• Gasoline is readily available.

A diesel unit may be preferred when:

• Continuous operation is expected.
• Higher hydraulic horsepower is required.
• The equipment operates under sustained load.
• Diesel fuel is standard at the site.
• Greater fuel capacity is needed.
• The application is commercial or industrial.

Foster manufactures both Honda gasoline-powered units and Kubota- or John Deere-powered diesel systems, allowing the prime mover to be matched to the application.

Diesel vs. Electric Hydraulic Power Units

Electric hydraulic power units are often preferred inside industrial facilities where reliable electrical service is available.

Electric systems can offer:

• Lower operating noise
• No onsite exhaust emissions
• Simple starting
• Lower routine engine maintenance
• Easy integration with plant controls

Diesel systems provide:

• Independence from the electrical grid
• Portability
• Outdoor operation
• Remote-site capability
• High hydraulic horsepower without large electrical service requirements

The correct choice depends on location, mobility, operating hours, available utilities, ventilation, and required hydraulic power.

Why Custom Engineering Matters

Two hydraulic applications may require the same flow and pressure but need completely different systems.

Differences may include:

• Duty cycle
• Number of functions
• Valve sequence
• Environmental exposure
• Cooling demand
• Tank capacity
• Load-holding requirements
• Portability
• Automation
• Noise limits
• Operating temperature
• Physical dimensions

Foster can modify basic hydraulic power units or design complete systems around the customer’s operating requirements. Available customization includes pump selection, tank capacity, cooling, heating, control valves, coatings, frames, cages, containment, and control methods.

Why Choose Foster Hydraulics?

Foster Manufacturing has specialized in hydraulic equipment since 1978 and remains a family-owned, second-generation manufacturer. The company builds custom electric, gasoline, and diesel hydraulic power units for customers throughout the United States.

Foster diesel hydraulic power units are available with:

• Kubota and John Deere diesel engines
• Fixed-displacement gear pumps
• Pressure-compensated piston pumps
• Thermostat-controlled heat exchangers
• Reservoir heaters
• Manual or solenoid control valves
• Custom hydraulic circuits
• Larger fuel tanks
• Larger hydraulic reservoirs
• Protective cages
• Crane-lifting provisions
• Forklift-accessible skids
• Flow meters
• Drip-containment pans
• Marine-quality powder coating
• Certified welding
• Quick couplers
• Mobile and portable configurations

Each unit can be tailored around the required flow, pressure, duty cycle, control sequence, environment, and physical installation.

Frequently Asked Questions

What size diesel hydraulic power unit do I need?

The correct size depends on required GPM, operating PSI, pump efficiency, duty cycle, and the number of functions operating at one time. Hydraulic horsepower should be calculated before selecting the engine.

How much horsepower is needed for a hydraulic pump?

Use:

GPM × PSI ÷ (1,714 × efficiency) = required horsepower

Additional capacity may be needed for starting conditions, altitude, temperature, accessory loads, and engine-performance characteristics.

Does a larger hydraulic pump always produce more pressure?

No. A larger-displacement pump normally produces more flow at the same RPM. System pressure is determined by load resistance and limited by pressure-control devices such as relief valves or pump compensators.

Can a diesel hydraulic power unit operate multiple functions?

Yes. Multiple functions can be operated with sectional valves, solenoid manifolds, tandem pumps, flow dividers, priority valves, or pressure-compensated systems. The circuit must be designed around whether the functions operate separately or simultaneously.

Can Foster build a closed-center diesel hydraulic system?

Yes. Foster offers pressure-compensated systems and multiple control-valve configurations for custom diesel hydraulic units.

Are Foster diesel units portable?

Foster offers compact, skid-mounted, forklift-accessible, crane-lift, and mobile-style configurations. Portable systems can be customized for the customer’s transportation and operating requirements.

Can a diesel hydraulic power unit be used in cold weather?

Yes, but oil viscosity, starting conditions, battery capacity, warm-up procedures, and reservoir heating must be considered. Foster offers reservoir heaters and thermostat-controlled equipment for demanding operating environments.

What type of hydraulic pump should I choose?

A gear pump is often appropriate for a straightforward open-center system. A pressure-compensated piston pump may be better for a closed-center system, variable demand, reduced standby losses, or multiple hydraulic functions.

How often should the hydraulic filter be changed?

Filter service depends on operating hours, contamination levels, filter capacity, oil condition, and the manufacturer’s maintenance schedule. A filter indicator and regular oil inspection are recommended.

Can Foster add custom valves and controls?

Yes. Foster offers various control-valve configurations, manual and solenoid controls, flow controls, selector valves, and custom circuits for industrial, mobile, and specialty applications.

Request a Custom Diesel Hydraulic Power Unit

The best diesel hydraulic power unit is not simply the one with the largest engine or the highest pump flow. It is the system that delivers the required hydraulic performance while controlling heat, fuel consumption, contamination, noise, weight, and operating cost.

Foster Hydraulics can build a diesel hydraulic power unit around your specific:

• Flow requirement
• Operating pressure
• Duty cycle
• Hydraulic circuit
• Valve configuration
• Reservoir capacity
• Fuel capacity
• Cooling requirement
• Environmental conditions
• Portability needs
• Control method

Contact Foster Hydraulics to discuss your application and request a quote for a custom-built diesel hydraulic power unit.

Foster Hydraulics
Foster Manufacturing Corporation
1836 Oakdale Avenue
Racine, Wisconsin 53406
262-633-7073
info@fostermfgcorp.com

Custom Hydraulic Power Units — Built Fast. Built Right.

No two projects are alike, and that’s why we offer fully customizable diesel hydraulic power units. From pump specifications and tank size to control valve configurations and specialized coatings, our team will design and build a system that meets your precise operational requirements. Optional features such as marine-grade powder coating, protective cages, crane lift points, and advanced flow meters ensure your power unit is ready for any job site. We also offer mobile and compact diesel units for projects that require portability without sacrificing performance.

Each diesel hydraulic power unit is designed for maximum efficiency, with features like electronic engine control consoles, heavy-duty skid platforms with forklift access, and electric start systems. Our standard models are available with multiple pump options—ranging from 10 GPM at 3,000 PSI to 15 GPM at 2,000 PSI—making them ideal for applications such as dewatering pumps, walking floors, and other high-demand hydraulic needs. With lead times as short as 7–10 business days for standard builds, we’re committed to delivering both speed and quality.

At Foster Hydraulics, we’ve been manufacturing high-performance hydraulic equipment since 1978. As a second-generation family-owned business, we combine decades of expertise with a dedication to customer satisfaction. Every diesel hydraulic power unit we build is backed by our commitment to quality, customization, and service you can trust. Contact our team today to discuss your application and get a quote for a unit built to work as hard as you do.