Hydraulic Power Unit Sizing Guide
Hydraulic power unit sizing: check pressure, flow and duty cycle, estimate hydraulic power, and prepare the inputs for an engineering review.
Read the guideENGINEERING KNOWLEDGE
Hydraulic power unit guide and questions
Practical answers on energy savings, product selection, installation, delivery and maintenance for engineers and purchasing teams.
Same-Boundary Energy Verification
Measure electricity use before and after an upgrade with the same machine, output and duty cycle.
Read the guideHydraulic Power Unit Factory Acceptance
A project record checklist for hydraulic power unit factory acceptance and document review.
Read the guideHydraulic power unit components and working principle
What is a hydraulic power unit?
A hydraulic power unit supplies oil flow to a hydraulic circuit. A typical assembly brings together a drive motor, pump, reservoir, valves, filtration and monitoring. The components of a hydraulic power unit must be checked against the selected model and circuit.
How does a hydraulic power unit work?
The motor drives the pump; valves direct and control flow to the machine actuators. Pressure depends on the load and circuit settings. In Shanchuan’s suitable pressure-holding applications, an accumulator supports the hold while the motor stops, with replenishment triggered by pressure feedback.
How does a hydraulic power pack work in a machine?
Power pack and power unit describe the assembled hydraulic supply here. Hydraulic power pack uses on this site include CNC clamping, casting fixtures and EPE forming. Separate the flow needed for movement from the pressure needed during a hold when discussing an application.
SALES & ENGINEERING FAQ / 50 QUESTIONS
50 answers across 9 purchasing topics.
From energy savings and equipment selection to installation and maintenance: practical answers for engineering, purchasing and service teams.Updated: 2026-10-05
Principle and energy
01How does this energy-saving unit work, and why does it use neither a servo motor nor an inverter?
The unit uses a standard induction motor, a pump, a PLC and an accumulator. The pump supplies oil during motion. It stops during a pressure hold and restarts when pressure falls below the set level. The PLC reads pressure and controls this cycle.
This design does not need a servo motor or an inverter. The right choice still depends on the machine. For constant flow or fast changes in pressure and speed, compare other supply options.
02What maintains pressure when the motor stops, and will recharging be frequent?
The accumulator stores hydraulic energy and supplies oil during the hold. The motor restarts when pressure falls below the lower setpoint.
Leaks, oil demand, usable accumulator volume and the pressure band affect how often it restarts. Frequent starts call for a system check. Do not widen the pressure band without checking the minimum pressure needed to hold the load.
03How is the advertised 90%–95% saving calculated: idle testing or whole-machine measurement?
Measure electricity use in kWh before and after the upgrade. Use the same machine, output and working cycle.
Saving = (energy before − energy after) / energy before × 100%. The baseline must be greater than zero.
Measure the hydraulic unit and the whole machine separately. This shows how much the unit contributes to production costs. We can help agree the measurement points, cycles and test period.
04Which duties can achieve savings above 90%, and does it suit every hydraulic machine?
Short movements, long pressure holds and low oil demand during holding offer scope for savings. A result above 90% also depends on the old unit’s standby losses, motor run time and power used by other parts of the system.
We can assess your machine using measured data. Constant high flow, frequent movement or large leaks need a separate calculation.
05Does “almost zero temperature rise” mean a hot casting or forging workshop needs no cooler?
No. Our cases show lower oil temperatures. They do not mean the unit generates no heat.
Choose cooling based on workshop temperature, the permitted oil temperature, motion time and heat from the components. Then test the unit under load. Removing a cooler in one project does not mean it can be removed in every installation.
06Will frequent starts damage the motor, and how stable is PLC pressure control?
Check the motor and switching components for the planned number of starts, load and temperature. PLC control still allows some pressure variation.
Agree the allowed pressure drop, recharge band, sensor accuracy and fault interlocks. Test the pressure trace, starts per hour and motor temperature. These checks define the limits for the chosen machine; there is no single start rate or accuracy figure for all duties.
07Will stopping the motor delay clamping or mould opening?
Response depends on the pressure at the start command, stored oil, valves and recharge controls. Test the time from command to completed movement. Use the lowest allowed pressure, highest load and repeated cycles.
Check that the result meets the machine’s cycle time. An accumulator does not by itself remove all delay. Its size, pipework or supply controls may need changes.
Technical reference: Parker accumulator catalogs and selection resources
Application fit
08Is a short holding phase suitable, and what is the minimum useful holding ratio?
A short hold can be assessed, but the saving may not justify the investment. No universal minimum holding ratio is established. Record motion, holding and standby times plus energy over a representative shift, then compare intermittent holding, servo and variable-displacement options using the actual duty profile.
09Can it directly replace my old unit without changing cylinders, valves or pipes?
Some of our projects keep the existing cylinders and valves. Reuse depends on pressure ratings, leaks, seals, ports, pipe condition and controls.
Send the hydraulic diagram, machine signals and dimensions. The proposal can then state which parts stay, which need replacement and which must be added.
10Can multiple circuits or cylinders operate at the same time?
Tell us which circuits or cylinders must work at the same time. A model code alone does not show this capacity.
List each load, timing, combined flow and any separate holding needs. We check pump supply, usable stored oil and valve control. This helps prevent one circuit from reducing the pressure available to another.
11Can it operate in dusty, hot or humid workshops, and is the tank dust-protected?
The new catalogue does not specify a universal ambient range or IP rating. Provide temperature, dust, humidity and condensation conditions; confirm motor, controls, corrosion protection, filtration and cooling against the selected model instructions and drawings.
12What pressure and flow ranges are available?
All nine catalogue models list 4.5 MPa rated pressure and 4.5–6 MPa system pressure. Vertical SC-QT: 16 L/min and 20 L tank. Horizontal SC-QT: 20 L/min and 40 L tank. Listed pressure and flow do not imply continuous simultaneous operation; confirm the operating point against the motion and holding cycle.
13Can the accumulator supply a brief high-flow demand for fast motion?
It can be assessed as a short-duration supply source. Calculate required oil volume, delivery time and allowed pressure drop. Nominal volume is not usable oil volume; pre-charge conditions, minimum working pressure, valves and lines also matter. Provide cylinder dimensions, stroke, timing and load for sizing and cycle verification.
Technical reference: Parker accumulator catalogs and selection resources
14Is it only for retrofits, or can it be supplied with new machinery?
Both new-machine integration and retrofit requests can enter engineering review. New builds allow hydraulic, electrical, mounting and acceptance interfaces to be agreed during design. Retrofits require review of the existing circuit, interlocks, pipe condition and downtime window. Final configuration and responsibilities follow the technical agreement.
Comparing solutions
15What are its advantages and limitations compared with a servo hydraulic unit?
Intermittent holding stops the pump during a hold. It uses stored oil and start/stop control. Long holds with low leakage are a good reason to assess this approach.
Compare servo supply when pressure or flow must change continuously, or fast response matters. Use the same working cycle to compare performance, energy, maintenance and purchase cost. Neither design is best for every machine.
16Servo hydraulics can also save energy, so why choose this approach?
Choose by duty rather than assuming that a standard motor is always cheaper or more efficient. Long clamping holds are candidates for intermittent operation. Continuous precision control of pressure, flow or speed calls for comparison with servo and other alternatives. Use the same representative machine or load profile to make the decision.
17If a conventional unit costs less initially, is the higher purchase price worthwhile?
Compare total cost: purchase, installation, retrofit downtime, energy, maintenance and spares. The investment is worthwhile only if measured or defensibly estimated operating savings cover the additional cost. Short operating hours, an efficient existing unit or an extensive retrofit may favour keeping the conventional solution.
18Are spare parts standard off-the-shelf items, unlike expensive servo repairs?
The company cases describe standard components, but matching nominal specifications alone does not make replacements interchangeable. Check the actual bill of materials, interfaces, ratings, electrical data and compatibility. Request approved alternatives, critical spares and pricing rather than assuming that every repair will be cheaper than a servo-system repair.
19Are standard induction motors immune to voltage fluctuations that affect servo or inverter systems?
No. A standard induction motor still requires a suitable supply, including voltage, frequency and phase conditions. A servo drive is not simply a conventional inverter. Check the site supply against the selected motor and control-component specifications and agree the protective configuration; no universal voltage tolerance is stated here.
20How should we choose between a variable-displacement pump and intermittent accumulator holding?
Start with pressure and flow over time. Long holds with little make-up oil are candidates for intermittent accumulation; sustained but varying demand warrants comparison with variable-displacement and variable-speed supply. Assess minimum pressure, response, leakage, noise, maintenance and total cost, not motor nameplate power or headline savings alone.
Cost and payback
21How much does the unit cost, and how much more is it than a conventional unit?
No publishable standard price list or fixed premium is available. A quotation needs pressure, motion flow, holding time, tank, supply, controls, quantity and destination. Compare itemised standard equipment, customisation, documents and services using the same scope of supply.
22Can you calculate electricity savings and the investment payback period?
Start with measured data from your machine. Monthly electricity saving = kWh saved at the same output × your tariff.
Add verified maintenance savings and subtract any new maintenance costs. This gives the net monthly saving. Simple payback = investment / net monthly saving. There is no payback when net savings are zero or negative.
For a retrofit, include installation and downtime costs. For a new purchase, use the extra cost over the alternative. This simple calculation leaves out financing and the time value of money.
23What costs besides electricity might be reduced?
Potential categories include cooling energy, oil and filters, seals, repair labour and downtime, but each needs baseline and follow-up evidence. Lower temperature does not automatically double oil life, and case-specific maintenance gains are not universal. Do not count cooler energy twice if it is already inside the metered boundary.
24Can we test one machine before committing to a larger order?
A pilot on one machine can help you decide, if the trial is feasible and its scope is agreed.
First agree the machine, output, meters, test period and pass criteria. Define which equipment the measurement includes and who pays each cost. Keep energy, cycle, pressure and oil-temperature records from both runs. Trial fees, returns and later orders need a separate written agreement.
25Does the quotation include installation, commissioning and transport?
Check each item in the written quote: the unit, controls, custom ports, documents, packing, freight, installation, commissioning, training and taxes.
Remote help or a site visit is included only if stated. For export orders, also agree trade terms, import costs and who supplies each document.
Retrofit and delivery
26How long will retrofit downtime and commissioning take?
A fixed duration cannot be stated before reviewing the machine. Scope removal, pipe work, wiring, program integration, cleaning/filling and loaded acceptance. Drawings, parts and off-machine integration can be prepared beforehand where feasible. Agree the actual downtime window and contingency allowance against the retrofit task list.
27Does retrofitting require changes to the host-machine PLC program?
It may require program changes or integration through agreed signals, depending on the existing architecture. Review start permission, pressure-ready, clamp confirmation, alarms, emergency stop and interlocks. A separate unit PLC does not remove the need for machine-level validation. Agree changes, backups, access and acceptance responsibilities.
28What are the lead times for standard and customised units?
Tell us the model, quantity and target arrival date. We will prepare production and dispatch milestones around the configuration, key components and testing requirements. For customised units, we agree drawings and interfaces before assembly and factory acceptance.
29What mounting space is needed, especially for the accumulator?
The catalogue lists 500×300×400 for vertical SC-QT and 660×380×438 for horizontal SC-QT (L×W×H), without dimension units. Confirm units, ports, mounting and clearance for pipework, controls, cooling and accumulator service against the selected model drawing.
30Are units pressure-tested, energy-tested or run for 72 hours, and is a test report available?
Our delivery process includes checks of no-load operation, pressure, motor start/stop and holding. We also check leaks, noise, temperature and electrics, and keep a factory inspection record.
This does not mean every unit has a 72-hour energy test. The 72- and 168-hour periods on our case pages relate to those projects. Agree any extra load, energy or third-party tests and reports before ordering.
Warranty and service
31What is the warranty, and does it cover the accumulator and pressure sensor?
The new catalogue does not state a warranty duration for these models. Confirm the start date, accumulator and sensor coverage, repair transport and service arrangements in the model-specific supply proposal.
32Is maintenance straightforward, with no proprietary or custom spare parts?
Serviceability depends on local skills, diagnostic documentation and spare availability. An absence of proprietary parts is not established. Confirm the actual motor, pump, valve, sensor and control BOM, replacement rules and critical spares. Accumulator, safety-circuit and program work must follow the relevant instructions and personnel requirements.
33Is support remote or on-site, and how quickly can service reach another region?
Our service process starts with remote assessment, followed by parts repair/shipping or site service as needed. Provide model, serial number, alarms and safely obtained photos/video. No universal on-site response time is documented. Agree coverage area, response arrangements, spare transport, attendance costs and overseas support.
34What needs periodic maintenance, and is the unit maintenance-free?
The unit needs maintenance. Check oil level and condition, filters, leaks, pipes, motor cooling, electrical connections, pressure sensors and the accumulator.
Set intervals using operating hours, workshop conditions, oil tests and component instructions. Ask for a maintenance schedule. Investigate unusual heat, frequent recharge or loss of holding pressure.
35How often must the accumulator be checked, and is annual statutory inspection required?
Routine condition/pre-charge checks differ from legally required inspection. The applicable regime depends on actual equipment characteristics and the place of use and must be established by the responsible equipment manager and appropriate specialists. No universal annual-inspection rule or exemption is established here. Request the nameplate, component documents, maintenance instructions and project inspection plan.
36Can production continue in a temporary mode after a PLC fault?
Do not assume a fallback mode exists. Only a documented, validated backup or manual mode may be used through its authorised procedure, preserving pressure, clamping and machine interlocks. Do not bypass sensors, emergency stops or alarms. Specify fault behaviour, recovery procedures and program backups during engineering review.
Cases and documentation
37Are there industry case studies, and can we visit a working installation?
Explore our Chengdu Linxiang workholding, Chongqing Zhicheng casting and Chongqing Rixin EPE forming projects. Compare their duty cycles, pressures and environments with your machine, then discuss a suitable configuration with us. For a site visit, we can help coordinate the host’s production schedule and permitted access.
38Can we obtain site photos and raw test data for Linxiang, Zhicheng and Rixin?
Tell us which project, operating conditions and documents you would like to review. Our team will check project records and customer permissions, then confirm the available site photos, test records and technical information.
39Are written acceptance reports and testimonials available for public use?
Our case pages share project results and customer feedback. Contact us if your internal review requires further acceptance documentation. We will check the available records and coordinate customer permission and any necessary redaction.
40Which reports or qualifications are available, and can the product meet CE requirements?
We can provide our enterprise standard and product technical documentation. For an export project, tell us the destination, model and supply scope. We will review applicable requirements, available documents and any additional testing or assessment with you, then define cost and timing. CE documentation and implementation are confirmed for each export project.
41Can you supply hydraulic schematics and component lists for technical review?
Ask for the hydraulic diagram, parts list, electrical drawings, ports and control description needed for your review.
Our delivery process includes assembly to drawings and supporting instructions and electrical diagrams. It does not mean every design file is open for release. Agree who will use the documents, their purpose and revision, when they are needed, and any confidentiality terms.
Accumulator safety
42Is the accumulator safe, and are relief valves and protective functions included?
An accumulator stores energy; safety cannot be assumed regardless of design or use. Verify pressure ratings, overpressure protection, isolation, pressure-release provisions, mounting and maintenance against drawings and the BOM. The actual relief/safety block configuration must be confirmed. A PLC alone does not establish a safety function; use suitably trained personnel.
43How is accumulator pressure handled after power loss?
Stored hydraulic pressure can remain after power is lost. The design must define whether to hold or release it in a controlled way. A sudden release can move a clamped or suspended load.
Before service, follow the machine’s isolation procedure. Secure the load and verify that stored energy is controlled. Never loosen a fitting to check pressure. Confirm any automatic pressure-release function in writing.
44How long does the accumulator last, and when should its bladder be replaced?
There is no universal life or bladder-change interval. Cycles, temperature, pressure ratio, fluid/material compatibility, pre-charge condition and contamination affect service life. Follow the selected model instructions and inspection records. Have qualified personnel diagnose frequent recharge, reduced holding or leakage rather than assuming that repeated charging or a case-derived lifetime is appropriate.
45Can excessive internal leakage cause frequent motor starts?
Yes. More leakage usually increases holding-phase make-up demand, potentially raising starts and energy use. Check cylinders, valves and circuit leakage, then measure pressure decay and recharge frequency. Decide whether to repair leakage, revise sizing or change the supply strategy while preserving required safety and cycle performance.
Operation and configuration
46What is the operating noise level, and how much lower is it than a conventional unit?
No universal noise guarantee is established. Company cases report 79→41 dB for Linxiang and 76→40 dB for Rixin, without complete distance, weighting or background-noise details. These are not standardised acoustic results. Agree position, operating phase, load and method before comparing before/after readings.
47What hydraulic oil is required, and can existing oil be reused?
The new catalogue does not specify hydraulic oil. Confirm viscosity, base oil, additives, seal compatibility, temperature and cleanliness against the selected model instructions and supply proposal. Do not reuse or mix oils without confirmation.
48Is an explosion-protected version available?
Explosion protection requires a dedicated engineering assessment. Contact us to discuss a possible supply configuration. Provide destination, area classification, gas/dust and temperature conditions for specialist review. Replacing the motor alone does not establish whole-unit suitability. Confirm supply capability and documentation before quotation.
49Can one hydraulic unit supply several fixtures or machines?
We can assess a shared supply for several fixtures or machines. Send the load and timing for each one.
The review covers combined flow, branch pressure ratings, separate holding, isolation and fault effects. A fault at one station may affect others, so production continuity matters too. A multi-station model code does not mean unlimited machine capacity.
50Can pressure and holding time be changed on a touch panel?
That depends on the control configuration; a touch panel is not documented as standard on every model. If provided, define editable settings, access rights and engineering limits. Changes to pressure bands, recharge logic or holding time require rating and machine-cycle checks. Specify interface language, permissions, backups and change records before ordering.
ENERGY INTO VALUE
Less idle running. More value.
Make each holding phase count. Stop the motor after motion, then recharge when pressure reaches the set threshold, reducing energy use and heat from continuous idle running.
Save 75% or more in short-motion, long-hold applications. Turn reduced electricity use into lower running costs and get more value from every clamping cycle.
Annual electricity cost savingkWh avoided × electricity tariff
Review the savings potential of your machine →Hydraulic power unit FAQ and holding basics
Use this hydraulic power unit FAQ to connect purchasing questions with engineering inputs. Hydraulic pressure holding basics start with the load, leakage, holding time and replenishment logic. For hydraulic power unit questions about a particular machine, provide its circuit and operating conditions alongside the model code.