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SM4 Hydraulic Rotary Actuator FAQs

The SM4 is rated up to 250 bar (3,625 psi), but can operate efficiently from low pressures.

SM4 rotary actuators are designed for a maximum operating pressure of 250 bar, but their low friction seals allow the rotary actuator to operate from as low as 10 bar (145 psi).

Standard angles include 90º, 180º, 270º, and 360º, with low, configurable backlash.

The SM4 rotary actuator can handle all standard rotations, with any intermediate angle (including >360º) available by limiting or increasing stroke length. Backlash is typically around 20 angular minutes. Custom models are available with backlash down to about 5 angular minutes for higher position accuracy.

The SM4 is designed to handle high radial and axial loads due to its four-point bearing.

The four-point bearing is designed to withstand significant radial and axial loads, making it suitable for applications where the actuator shaft carries the load directly (such as boom pivots or workplatforms). Low axial hydraulic load on the drive shaft (due to a small pressure differential) further protects the bearing and extends service life.

Use standard HLP mineral oil, typically -25ºC to +70ºC (-13ºF to 158ºF), with good filtration.

Hydraulic fluids: SM4 actuators are designed for mineral oil hydraulic fluids of group HLP as per DIN 51524 part 2 (VDMA 24318) with viscosity roughly 16 to 68 cSt in the 40ºC to 60ºC (104ºF to 140ºF) range.
Operating temperature: The typical operating temperature is between -25ºC to +70ºC (-13ºF to 158ºF) given that the above fluid specifications are met.
Filtration Levels: The system should maintain cleanliness better than ISO 4406 class 19/15, typically via ≤25 µm pressure/return filtration.

Hydraulic Rotary Actuators – SM4

The Eckart SM4 rotary actuator is a heavy-duty and highly-customizable rotary actuator designed for the toughest and most-demanding applications.

Because of its torque, angle of rotation, pressure range, positioning accuracy, stability of position, type of attachment, and its dimensions, the Eckart SM4 rotary actuator can be used in a wide range of applications. Not only is the SM4 a compact and robust unit, but it is also wear-resistant and efficient. The SM4 can be configured with an industry-leading fine and controllable end cushioning curve. Additionally, the SM4 unit can be driven via “black and white” or with proportional, control, and servo valves. For the purpose of subsequent driving, the piston end-positions at the linear cylinder and at the rotary actuator can be scanned via electronic end-position acknowledgement mechanisms. Ultimately, with the SM4, you have a high-performing product that is both robust and compact, allowing for optimal adaptation depending on your specific requirements.

Hydraulic Rotary Actuator Standard Features:

Torque output to 750,000 in-lb (85,000 Nm)
Pressure rating at 3,625 psi (250 bar)
Standard rotation: 90°/180°/270°/360°
Externally adjustable end stop ± 5°
Wear resistant moving parts
Four-point contact bearing to withstand extreme radial and axial loads
Adjustable home position
Tight backlash of 20 angular minutes

Hydraulic Rotary Actuator Optional Features:

End cushioning including sophisticated damping curves
Tighter backlash as low as 5 angular minutes
Position indication through encoders or proximity switches
Drive shaft configurations, such as spline shaft, tooth hub, hollow shaft, key shaft, etc.

SM4 Configurations

The SM4 rotary actuator can be customized to your exact application with options like single or dual-end drive shafts, rotation past 360°, reversed turning direction, corrosion-resistant materials and protection suitable for sea or saltwater environments.

Refer to the charts below to configure drive shaft, mounting, valve plate, bottom configuration, and accessories.

Custom drive shaft options for Eckart SM4 hydraulic rotary actuators.

Drive Shaft	Reference
Shaft, smooth
Shaft, with keys
Splined shaft
Gear shaft
Shaft with polygon (conical)
Hollow shaft with keyways
Hollow shaft with gear hub or with multiple- splined hub
Hollow shaft with square end
Flanged shaft (E3 ONLY)

Custom mounting options for Eckart SM4 hydraulic rotary actuators.

Foot Type	Reference
With foot
Flange-flattened
Flange with fixing grooves
Flange according to DIN ISO 5211

Custom valve plate options for Eckart SM4 hydraulic rotary actuators.

Valve Plate Type	Reference
Valve (1) and valve plate (2)
Stop valve plate (1), cushioning plate – all other types of thread possible (2), standard connection bores – all other types of thread possible (3)

Custom accessory options for Eckart SM4 hydraulic rotary actuators.

Accessory Type	Reference
Proximity switch – pressure resistant (to approx. 25º)
Pressure absorber
Measuring connection
Bleed valve with hose liner
Locking screw

Custom bottom options for Eckart SM4 hydraulic rotary actuators.

Bottom Type	Reference
Angle sensor, potentiometer with coupling and mounting housing
Locating pin smooth (A) or locating pin with thread (B), cam (1), clamping ring with proximity switch (c) or clamping ring with mechanical switch
Angular adjustment (ex. from 90º to 180º)
Agraduated adjustment (ex. from 0º to 90º)
With second flange, on base, with foot on base
With large flange at center
With adjusting cylinder for intermediate angles of rotation
With second exit shaft (also possible with the types a to j), see SM4 catalog on pg. 4
With outside square end for manual operation

Technical Data

Angle of Rotation	standard 90º/180º/270º/360º and any intermediate angle, even above 360º
Medium	recommended: mineral oil of group HLP/DIN 51524, page 2 and VDMA page 24318; others on request
Min. Operating Pressure Required	72.5 to 145 psi (5 to 10 bar)
Max. Allowable Operating Pressure	3,625 psi (250 bar) / higher on request
Installation Position	as required, provided that adequate air bleeding is provided
Temperature Range	-13ºF to 158ºF (-25ºC to 70ºC) / higher or lower on request

Size (piston-Ø)	40	50	63	80	100	125	140
Max Torque lbf-in \| [Nm]	1593 [180]	3319 [375]	6505 [735]	11505 [1300]	23896 [2700]	47792 [5400]	74346 [8400]
Spec Torque lbf-in/psi \| [Nm/bar]	0.44 [0.72]	0.92 [1.50]	1.79 [2.94]	3.17 [5.2]	6.59 [10.8]	13.18 [21.6]	20.48 [33.6]
Absorption Volume in^3/1º\| [cm^3/1º]	0.010 [0.170]	0.021 [0.352]	0.041 [0.669]	0.160 [2.624]	0.314 [5.154]	0.477 [7.819]	0.723 [11.846]
Max. Admissible Rotation Time Per 90º (without load) [s]	0.13	0.18	0.24	0.26	0.43	0.55	0.63
Weight ca. 90º lbs \| [kg]	12.13 [5.5]	19.40 [8.8]	25.35 [11.5]	46.30 [21.0]	81 [37]	143 [65]	202 [92]
Weight ca. 180º lbs \| [kg]	13.23 [6.0]	21.16 [9.6]	28.66 [13.0]	50.71 [23.0]	92 [42]	163 [74]	233 [106]
Weight ca. 270º lbs \| [kg]	14.33 [6.5]	22.05 [10.0]	30.86 [14.0]	56.22 [25.5]	103 [47]	185 [84]	264 [120]
Weight ca. 360º lbs \| [kg]	15.43 [7.0]	24.47 [11.1]	34.17 [15.5]	60.62 [27.5]	114 [52]	211 [96]	295 [134]
Max. radial load FR lbf \| [KN]	3250.0 [1.45]	696.9 [3.10]	1079.0 [4.80]	2203.1 [9.80]	3821.7 [17.00]	5745.1 [25.60]	7193.9 [32.00]
Max. radial load FAE lbf \| [KN]	1353.4 [6.02]	2839.5 [12.64]	3299.3 [14.55]	5472.3 [24.35]	8829.9 [39.27]	13785.8 [61.35]	20564.0 [91.50]
Max. radial load FAA lbf \| [KN]	224.8 [1.00]	472.1 [2.10]	854.3 [3.8]	1111.2 [4.95]	1281.4 [5.70]	1550.2 [6.90]	2023.3 [9.00]

Size (Piston-Ø)	160	180	200	225	250	300
Max Torque lbf-in \| [Nm]	113290 [12800]	173475 [19600]	230120 [26000]	303490 [34300]	424836 [48000]	752316 [85000]
Spec Torque lbf-in/psi \| [Nm/bar]	31.25 [51.2]	47.83 [78.4]	63.59 [104.2]	83.66 [137.2]	117.17 [192.0]	207.48 [340.0]
Absorption Volume in^3/1º\| [cm^3/1º]	0.723 [11.846]	1.058 [17.342]	1.466 [24.014]	1.961 [32.162]	2.731 [44.767]	4.821 [79.028]
Max. Admissible Rotation Time Per 90º (without load) [s]	0.73	1.00	1.24	1.50	1.78	2.10
Weight ca. 90º lbs \| [kg]	315 [143]	434 [197]	539 [245]	753 [342]	1190 [540]	2151 [976]
Weight ca. 180º lbs \| [kg]	363 [165]	496 [225]	630 [286]	868 [394]	1399 [635]	2503 [1136]
Weight ca. 270º lbs \| [kg]	412 [187]	588 [267]	720 [327]	983 [446]	1567 [711]	2858 [1296]
Weight ca. 360º lbs \| [kg]	458 [208]	665 [302]	811 [368]	1097 [498]	1757 [797]	3408 [1546]
Max. radial load FR lbf \| [KN]	9350.7 [41.60]	11915.9 [53.00]	14002.7 [62.30]	14634.3 [65.10]	15392.4 [68.50]	19604.6 [87.20]
Max. radial load FAE lbf \| [KN]	28255.1 [125.65]	34914.5 [155.25]	41922.2 [186.50]	42595.6 [189.40]	44539.7 [198.10]	57599.2 [256.25]
Max. radial load FAA lbf \| [KN]	3822.7 [17.00]	4945.8 [22.00]	6069.8 [27.00]	6513.5 [29.00]	7193.9 [32.00]	9216.2 [41.00]

Ordering Code

SM4 . 80 – 270º / SZ / Z1 / … / SO

3,625 psi (250 bar) series

Size (Piston-Ø)

Rotation (Standard) – 90º, 180º, 270º, 360º
Other rotations available on request.

Options – Omit for standard

Z1	end cushioning
Z4	long-range adjustable end stop
Z5	cam
Z6._	controls witch (1-mech. / 2-ind.)
SZ	locating pin
ZW	gear shaft DIN 5480
ZN	gear hub DIN 5480

Non-Standard Options – Omit for standard
(Consult factory)

Helical Spline Hydraulic Rotary Actuators:

Like all Eckart hydraulic rotary actuators, the SM4 is designed with helical spline technology. The actuator operates with a piston and a helical or sliding spline mechanism, which work in tandem to transform the piston’s linear motion into rotational movement.

High torque in a compact profile

Helical spline actuators deliver impressive torque within a compact construction, making them ideal for applications where space is limited.

Less risk of contamination and physical damage

Protective housing keeps all moving parts safe from debris and moisture, ensuring consistent operation in demanding environments, especially for mining applications.

Low maintenance and wear-resistant moving parts

All internal components are fully immersed in oil ensuring preventative wear.
Extended-period nitriding ensures a long service life of the rotary actuator.
Helical gears feature excellent sliding characteristics.

Reduced pinch points

Helical spline rotary actuators offer safer alternatives to linkages for the operator, since there are no exposed parts.

Standard Rotations:

Standard rotations are 90°, 180°, 270°,and 360°. Other rotations can be supplied on request by using the model with the next standard rotation up and limiting the stroke of the piston in accordance. Also available are special models with rotations in excess of 360°. Additional rotation is created by making the spline gears longer while maintaining the same diameter. The primary benefit to this type of product compared to alternative designs such as linkages using hydraulic cylinders (linear actuators) is its compact design.

Eckart is a supplier and rotary actuator manufacturer for various applications including construction, mechanical, marine, and industrial.