In a series circuit, oil leaving Motor 1's main outlet supplies Motor 2. The pump has to overcome both motors' pressure drops. In parallel, a junction separates the supply into two motor branches. Add their flow demands when sizing the pump. Torque depends on the pressure lost across each motor; shaft speed depends on the flow reaching it. Check any requirement for matching speeds separately.
Consider the outputs before drawing the hoses. Two separate conveyors may need independent speed controls. A shared belt constrains its rollers, while steering calls for different wheel travel around a bend. Describe those motions and any need to stop one shaft alone. Include deceleration if a moving load can drive the motor after the operator removes the command.
For an initial component search, BLINCE's hydraulic motor category provides the available family directions. Series suitability still depends on the selected configuration and its circuit. Neither the family name nor a photograph establishes the allowable pressure at a motor's outlet.
What changes when the motors share a pump
For fixed-displacement motors in steady motoring operation, the basic comparison is below. Bypasses, control valves, leakage and piping losses have to be added to the actual circuit.
Question
Motors in series
Motors in parallel
Where does pump flow go?
Through the first motor's main path, then the second
Into separate branches; total supply equals the sum of branch flows
What pressure must the pump provide?
The sum of motor pressure drops and circuit losses
Enough for the highest-pressure active branch plus its supply and return losses
What sets each shaft's speed?
Its displacement, useful through-flow and leakage
Its own branch flow, displacement and leakage
Can one motor run independently?
A separate approved bypass or control arrangement is needed
Individual branch control can provide independent operation
Is equal speed automatic?
Equal nominal displacement gives an ideal starting relationship only
An uncontrolled tee gives no specified sharing ratio
Which limit needs particular attention?
The upstream motor's outlet and case conditions
Available branch flow, load sharing and the control device's pressure loss
The second motor in a series circuit receives pressurized oil from the first motor's outlet. It can produce torque because pressure falls again across its own working chambers. The first motor therefore has pressure on both main ports. Its torque follows the difference between those pressures, rather than the reading at the pump alone.
For an ideal motor, with displacement D in cm³/rev and inlet flow Q in L/min:
n = 1,000 × Q / D
Here n is shaft speed in rpm. The corresponding ideal torque T in N·m, using motor pressure drop Δp in bar, is:
T = Δp × D / (20 × π)
Solving the torque equation for pressure gives Δp = 20 × π × T / D. For a real motor, allow for leakage in the flow estimate and mechanical losses in the torque estimate. The motoring equations are Q = D × n / (1,000 × ηv) and Δp = 20 × π × T / (D × ηhm), where ηv is volumetric efficiency and ηhm is hydraulic-mechanical efficiency. Take the values from the selected motor's curves at the point being calculated. A percentage taken at another speed or pressure can change the result.
The connection changes how these individual requirements reach the pump. In series, add the required pressure differences along the main flow path. In parallel, add the required branch flows. Write both budgets before comparing pump capacity. A pump's maximum pressure and maximum flow are not automatically available together at the required drive speed and power.
A worked comparison with the same two motors
This hypothetical comparison has four inputs:
Motor 1 displacement: 200 cm³/rev.
Motor 2 displacement: 200 cm³/rev.
Resisting torque at Motor 1: 200 N·m.
Resisting torque at Motor 2: 100 N·m.
Neither load drives its motor externally. Starting, acceleration, leakage and valve or pipe losses are excluded from this ideal first pass.
For Motor 1, 20 × π × 200 / 200 comes to 62.83 bar. Halving the torque for Motor 2 halves the required pressure difference, to 31.42 bar. The shared displacement has not made their loads equal.
Set pump delivery to 40 L/min for the first comparison. For parallel, assume a control holds the branch flows at 20 L/min each and accounts for the surplus pressure in the lighter branch. Substitute each motor's inlet flow into 1,000 × Q / 200 to obtain the table's speeds. The equal split is an imposed control condition; no sharing accuracy has been assigned to a tee.
Ideal calculation, same 40 L/min pump delivery
Series
Parallel with a controlled equal split
Flow into each motor
40 L/min
20 L/min
Speed of each 200 cm³/rev motor
200 rpm
100 rpm
Motor 1 required pressure drop
62.83 bar
62.83 bar
Motor 2 required pressure drop
31.42 bar
31.42 bar
Pressure across the motor network, excluding common losses
94.25 bar
At least 62.83 bar, with allocation losses accounted for
For the rest of the example, use a common target of 100 rpm. Series therefore takes 20 L/min through the pair, and controlled parallel takes 40 L/min total. The resisting loads stay at their original values. This supplies a common output for the pressure and power comparison.
The pump comparison needs a point on a curve: delivery at the required pressure and drive speed. Include efficiencies and path losses to locate it. If the documentation gives only two independent maxima, obtain the missing operating data before selecting the motor pair.
Read a series circuit as a pressure map
Use the same hypothetical pair at 100 rpm. Add an assumed 6 bar between the second motor's outlet and the reservoir. For this simplified pressure map, ignore the loss in the short connection between motors.
Starting at the reservoir end, the sums are 6 + 31.42 = 37.42 bar at the junction and 37.42 + 62.83 = 100.25 bar at the first inlet. Another hypothetical 6 bar in the supply-control path brings pump discharge to 106.25 bar.
Location in the example
Calculated gauge pressure
Pump discharge, including assumed supply loss
106.25 bar
Motor 1 inlet
100.25 bar
Motor 1 outlet / Motor 2 inlet, with connecting loss neglected
37.42 bar
Motor 2 outlet
6.00 bar
Reservoir reference
0 bar gauge
At Motor 1, subtract the two port readings: 100.25 − 37.42 gives the 62.83 bar used in the torque calculation. Using its inlet reading alone would overstate torque. Meanwhile, the 37.42 bar at its outlet must be checked against the selected build's permitted outlet pressure for this speed and duty.
If Motor 2's load increases, its required pressure drop increases. The pressure at Motor 1's outlet rises with it, and the pump needs to supply the larger total if both torques are to be maintained. A gauge at the pump cannot show how that total is distributed. Two working-port readings at each motor provide the local differences needed for the assessment.
For reverse operation, draw a second map with the arrows reversed. The motor previously at the tank end may now receive pump flow first. Check both port duties, including any brake-release, flushing and check-valve paths. Copy the port names from each motor drawing and establish shaft rotation from the stated viewing direction.
Outlet pressure and case pressure need their own limits
Vivoil's guidance on using its motors in series specifies its external-drain version and a suitable low-pressure drain connection. That requirement belongs to the documented Vivoil construction.
Keep separate rating entries for inlet pressure, outlet pressure, differential pressure, and case or shaft-seal pressure. Record duration and conditions alongside them. The external drain does not change the working-port ratings. For the example, an outlet limit is needed to assess the calculated 37.42 bar.
The diagrams on pages 19–20 of Danfoss's orbital-motor information show how different internal arrangements connect to the shaft seal. On the proposed machine drawing, label the working return, case drain and brake connection separately. A drain teed into the intermediate working line would see that line's pressure.
The Danfoss L and K Frame motor document, page 13, makes series operation conditional on system, charge and case-pressure limits, and calls for application assistance because bearing life is affected. Keep those model-specific restrictions attached to the configuration review.
Trace the power through the pair
For the stated 100 rpm duty, the sum of resisting torques is 300 N·m. Shaft power is:
Hydraulic kW can be found by multiplying bar by L/min and dividing by 600. The ideal series input is 94.25 × 20 / 600 = 3.14 kW. Supplying a constant-pressure parallel network with 40 L/min at a 62.83 bar supply-to-return difference gives 4.19 kW. In that example, a throttle in the lighter branch absorbs 31.42 bar at 20 L/min, equivalent to 1.05 kW. Choose another control architecture and its losses would have to be calculated from its own flow and pressure paths.
Include the assumed common supply and return losses of 12 bar used earlier. At 20 L/min, those losses add 0.40 kW in the series example. At the parallel circuit's total 40 L/min, the same assumed 12 bar adds 0.80 kW. The resulting comparison is:
Same hypothetical 100 rpm and shaft torques
Series
Parallel, with the stated throttling assumption
Combined ideal shaft power
3.14 kW
3.14 kW
Loss from common supply/return paths, assumed 12 bar
0.40 kW
0.80 kW
Additional light-branch throttling loss
0 kW in this simplified model
1.05 kW
Calculated pump hydraulic output
3.54 kW
4.99 kW
The fixed 12 bar is an illustration. Use each hose, fitting and cooler's actual loss curve for selection. Recheck the paths at the flow each option would carry, including the effect of motor and pump efficiency on drive input. The duration of each duty state is needed to turn the loss estimate into a heat assessment.
The parallel option may still be required for independent adjustment or fault recovery. Its controls have to be evaluated against that job. Include periods with one motor unloaded or stopped; they can occupy much more of a shift than the heaviest simultaneous duty. The 1.05 kW branch-loss figure above applies only to the stated throttling example.
Why equal flow does not guarantee equal motion
Compare two hypothetical ideal displacements:
Ideal operating point
200 cm³/rev motor
250 cm³/rev motor
Speed when each receives 20 L/min
100 rpm
80 rpm
Flow required for 100 rpm
20 L/min
25 L/min
Share of the combined 45 L/min needed at 100 rpm
44.44%
55.56%
Illustrative inlet demand at 100 rpm with ηv assumed to be 0.92
21.74 L/min
27.17 L/min
Series plumbing preserves the displacement ratio. Equal speed in parallel calls for different branch flows, as shown above.
For the last row, the ideal inlet demands were divided by an assumed ηv of 0.92. Total inlet demand becomes 48.91 L/min. Equal assumed efficiencies preserve the ratio. An actual divider inquiry needs the curves at the relevant oil condition and pressure; the two motors may have different leakage there.
Leakage routing changes the series flow balance. For a separate example, assign 20 L/min to Motor 1's inlet and 0.6 L/min to its external drain. With no other branches, the main outlet has 19.4 L/min left, a 3% reduction. Leakage that reaches the working outlet remains in that downstream supply. Draw its destination before subtracting it, so that oil is not counted twice as an external loss.
Check roller diameter as well as shaft rpm. Take two hypothetical rollers measuring 100 and 102 mm at their effective surfaces. At 100 rpm, circumference times rpm gives 31.42 and 32.04 m/min. Leave them free of mechanical coupling and the relative travel would reach about 3.14 m in five minutes. The calculated difference is 0.63 m/min at the surfaces. A shared belt prevents that free accumulation; forces, slip or actual speed must change to accommodate the constraint.
Name the controlled quantity in the tolerance. Roller surface speed, shaft rpm and angular position can require different corrections. Include the interval and load changes. A process accepting 5% speed variation gives the designer room that a fixed angular relationship over repeated starts does not.
Choose branch control around the required motion
An uncontrolled parallel connection is appropriate only where its actual flow behavior is acceptable. If one branch offers an easier flow path, the allocation can change as load changes. Equal hose lengths or matching nominal motor displacements do not establish a controlled split. Identify what device establishes each branch's flow over the operating range.
Sun Hydraulics' flow-divider technical tips, pages 1–2, distinguish dividing in one direction from dividing and combining for bidirectional motor duties. They also warn that operation below the specified flow range can lose the intended division, and that mechanically coupled outputs need attention to cavitation, lock-up and pressure intensification. These characteristics belong to the selected device and circuit; a label reading “50:50” does not describe every state.
Three operating requirements lead to different control checks:
Required behavior
Circuit question to resolve before selection
Two motors run together in one direction
What establishes the flow ratio, and does the divider remain within its rated input range during startup and slow running?
Two motors reverse together
Does the chosen device handle the return combining path, and what happens if one branch slows or stops?
Either motor runs by itself
How does the other branch isolate or bypass, and can the active motor receive its required flow without exceeding its speed limit?
A simple series chain ties the main flow paths together. Stopping one shaft may restrict the other unless a designed bypass or other operating path is provided. Add the bypass to the schematic and trace the remaining motor's flow with it open, closed and changing state. Those three sketches expose any change in pressure or speed that the extra path introduces.
Include gears, chains, the shared belt and any intermittent contact on the drawing sent for control selection. A rigid connection imposes shaft motion and can transfer torque between outputs. Contact through a belt or the ground can impose a different constraint as the machine operates. Mark when each constraint applies so that the proposed flow ratio can be checked against the mechanical motion.
Include stalled, starting and stopping states
Mark one shaft blocked on a copy of the schematic. On another, switch off one drive; on a third, reverse the command with the shafts still moving. Trace the bypasses and local relief paths on each copy. Normal-running data leaves those events open for review.
For series, compare the combined load demand with the pressure available. Once that demand exceeds the supply capability, the calculation no longer supports both requested operating points. Use the actual leakage and valve paths to investigate the resulting motion. Check the installed component and drive limits before considering any change to a relief setting.
For parallel, trace the fitted branch control with one shaft blocked and with its load removed. Include reverse flow. A priority control intentionally allocates supply differently from an equal-ratio divider. Independent valves introduce their own commanded states. The review needs the manufacturer information for the actual device and valve position.
Add breakaway torque for a loaded restart. A fitted brake needs its release event marked in the sequence, with the pressure available at that event. Use the motor's starting data for this check. The running-efficiency figures in the worked example leave breakaway performance unproven.
During a stop, a rotating load can keep driving oil through the motor. Mark that pumping direction on the stopping-state sketch. Have the circuit reviewer identify its replenishment and pressure-limiting paths, including passages a valve can isolate from the pump relief. Protection for this stored energy must be selected separately from the normal motoring calculation.
For an initial state review, a short worksheet is more useful than a single maximum-pressure figure:
State
What to specify
What the review should establish
Both running normally
Each speed, torque and operating duration
Flow allocation, motor pressure drops and heat generation
One shaft blocked
Which shaft, expected duration and commanded valve state
Where flow goes and which pressure limits govern
One motor intentionally stopped
Required behavior of the other motor
Isolation or bypass path and remaining speed control
Forward to reverse
Allowed pause and load condition
Flow paths, port pressures and control sequence
Deceleration or external drive
Load can overrun, required stopping behavior
Local pressure control, replenishment and holding requirements
Replacing one motor in an existing pair
Keep the existing motor's full suffix when comparing replacements. Alongside the flange and shaft drawing, compare displacement, port functions, outlet rating, drain arrangement and the relevant curves. The second motor and its controls form part of that comparison because the replacement changes one member of a working pair.
For a pair of nominally equal replacements, compare the curve entries for inlet flow at the required speed and torque. Keep the oil condition attached to those entries. Add the installed divider's ratio, flow range and direction capability. That comparison may reveal a missing operating point even when the headline displacement matches.
Record the circuit as found before ordering. Photograph both model tags, trace the main interconnecting line, identify each case drain and mark any bypass or cross-port assembly. A second small hose may be a brake-release or flushing connection, so identify it from the motor drawing. Preserve original port labels in the record; informal names such as “return hose” can mean different pressure duties in series operation.
BLINCE's orbital motor range can be used to start a configuration inquiry. A comparable family or displacement is a candidate for review. The selected drawing, operating limits and interface comparison are still needed before calling it a replacement for either motor in an existing pair.
What to send with a two-motor inquiry
A useful inquiry begins with the marked circuit and a description of the outputs. For a hypothetical roller machine, that could read: “Target 100 rpm at both rollers. Either roller must be able to stop alone. A common belt connects them while loaded.” The last two requirements need to be reconciled in the control design, so include when the belt is engaged and which stopping states are permitted.
For component selection, attach:
Identification: both motor tags or complete proposed codes.
Duty: the torque and rpm required at each shaft.
Supply: pump delivery at the intended drive speed and available pressure.
For existing equipment, put the port location and conditions beside the test value. Record valve position, shaft rpm and oil temperature with the pressure so the reviewer can locate that operating point on the motor's curve.
Add the permitted speed or position error over a stated interval. Mark forward and reverse duty, external driving loads and the response required after a stall. A drain-route sketch and the available motor limit sheets can complete the technical packet. Replacement inquiries also need the old and proposed interface drawings, with the dimensions and port functions identified.
Have a qualified technician take the working-port and case-drain readings through the designated test points. Follow the machine's approved procedure, secure its load and use instruments rated for the circuit. Opening an energized hydraulic line is unsafe; keep the lines closed throughout the test.
Send the marked two-motor circuit to BLINCE with a request for the candidate motor's drawing and limit sheet. Ask for confirmation of the outlet and case-pressure limits and the permitted series or parallel duty. Record any operating point or valve state that still needs review before releasing the motor order.
This article is a general engineering guide. Final component selection should be based on machine drawings, measured hydraulic data, working conditions, safety requirements, and confirmation from a qualified hydraulic engineer or supplier.
Blince Hydraulic Team
Blince Hydraulic is an industry-leading company dedicated to precision-engineered fluid power manufacturing and custom hydraulic solutions. Backed by decades of deep field expertise in industrial machinery and thousands of successful global deployments, our engineering team focuses entirely on high-performance hydraulic component manufacturing, including specialized orbital motors, high-pressure travel drives motor, and robust directional control valves. Our production infrastructure utilizes state-of-the-art multi-axis CNC machining systems and is fully ISO 9001 certified to guarantee repeatable volumetric accuracy across every single manufacturing run.
We deliver fast, highly dependable, and cost-efficient hydraulic solutions to heavy industry distributors, machinery OEMs, and maintenance crews across more than 150 countries. Whether your active project calls for a small-volume batch of customized shaft profiles or a large-scale production run of severe-duty cast iron gear pump, we configure our flexible production schedules to meet your target lead times with total pricing predictability. Partnering with Blince means securing maximum system efficiency, elite material quality, and uncompromised fluid power professionalism.
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