Hydrodynamic Fluid Couplings

Hydrodynamic Fluid Couplings


Alternativ styles of couplings are : HATECO SURE-FLEX – TEX-O-FLEX


Soft starts and smooth power flow with low starting torques. Hydro-flow is available in a variety of configurations to meet your requirements and exceed your expectations.

Hydroflow Coupling

Off load start Startup is free from long current peaks No equipment jamming
Soft start Automatic load distribution Protects machine from overloads andocks
Starting torque control Basic version starting at lower than 200% Delay chamber version starting at lower than 150% of nominal torque
Please provide full description of your application inc duty cycle and position of hydro dynamic coupler.

The Hydro-Flow hydrodynarnic coupling includes two basic elements: a pump A and a turbine B, which are both fitted with radial blades. Pump A is made of aluminium and is connected to the hollow shaft by splines. Ball bearings mounted on the hollow shaft are mounted in removable steel bearings, for easy maintenance.

The turbine B is bolted to a half-case C. The mating face is sealed. The aluminium delay chamber R may be bolted to half-ease C. The mating face is also sealed.

All the Hydro-Flow couplings are balanced dynamically and are all fitted with a fuse plug which releases the oil when the oil temperature exceeds +145C. Other protective devices may be provided on request.

HO versions

These versions are used as a baseline for all the other versions.

HV versions

This version includes a pulley whose cross-section and number of grooves are calculated to match the coupling power.

HE and HC versions

A SURE-flex or TEX-O-flex coupling flange is mounted on the coupling an allows the torque to be transmitted through a flexible element allowing misalignments.

The replacement of the flexible element can be realized without misalignment of the shafts.

The coupler can also be filled or drained with the driven machine loaded.

HP versions

A female PENCOflex hub is mounted on these versions in which the male hub engages.

HT versions

These are HATECO-type couplings which connect the coupling to the motor and the machine.


Off-load start

  • startup is free from the usual, long current peaks,
  • jamming is impossible,
  • automatic distribution of the load in case of joint drive by several motors.

Protection of the machine

  • – protection against continuous, light overloads,
  • – shock damping.

Starting torque control

Basic version: max. starting torque is lower than 200% of the nominal torque.

With the delay chamber: the starting torque is lower than 150% of the nominal torque.

Operating principles

Basic model

At startup, pump A which is integral with the motor forces the oil to move, under the centrifugal force.
The kinetic energy of the oil is transmitted to turbine B, thus creating a torque which tends to rotate the machine shaft.

In steady state, the slight difference in speed of turbine B with respect to pump A sustains the oil motion, which produces a permanent load on the blades, owing to the oil’s kinetic energy. The torque is thus maintained permanently.


  • the torque at the driving shaft is equal to the torque at the driven shaft,
  • the rotation speed of the driven element is always lower than the speed of the driving element (this difference is called “slip”),
  • the slip depends on the rotation speed, the transmitted torque and the quantity of oil in the coupling,
  • the power loss is equal to the slip percentage (2% for large sizes and 6% for small sizes),
  • the Hydro-flow coupling can rotate indifferently in any rotation direction,
  • the Hydro-flow coupling can be reversed under certain conditions (see Drive from the outside).

With a delay chamber


When the machine is not running, the delay chamber R contains some of the oil and thus reduces the quantity of oil contained in the primary rotor A.
When the motor is started, the torque available on the driven machine side is thus limited, and this allows the motor to rapidly reach its working speed and run rapidly across the high current consumption range. As soon as the motor is started, the oil slowly comes out of delay chamber R and fills the working system (rotor/turbine).
When the motor is running at its nominal speed, the maximum quantity of oil contributes to the torque transmission, so that there is only a minimum slip when the nominal torque is reached.


Effect on the electric motor

When a squirrel-cage motor, mounted directly on a machine with a high inertia is started, a substantial current surge is generated for a long period. This period may be divided into two parts: the motors rotor startup period and the machine startup period.

With an Hydro-flow coupling now fitted, the current absorbed by the motor during the machine startup phase is going to be reduced. With the Hydro-flow coupling, the motor can start as if there were no load. In this phase, the oil is not yet fully moving and the torque transmitted to the shaft of the driven machine is increasing slowly. This phenomenon is even more sensitive when a delay chamber is added. Thus the motor startup current IH or IR is reduced immediately. At motor speed nL, the machine starts when TH or TR > TL. The slipping of the coupling decreases gradually as the driven machines speed increases until the working speed nN is reached.

For starting machines with high inertia, such as conveyor belts and fans, the Hydro-flow makes it possible to use motors of smaller sizes (reduced starting current and improvement of the power factor cosj).

Then installing costly equipment becomes useless. Judicious selection of the oil filling level also makes it possible to influence the startup time.







t = time (S)
n = speed (min-1)
l = current (A)
T = torque (Nm)
S = slip (%)
M = motor
H = without chamber
R = with chamber
L = load
N = nominal

Effect on the driven machine

Curves TR and TH, for coupling with and without delay chamber, represent the torque transmitted to the driven machines shaft. The curves illustrate the favourable impact the Hydro-flow coupling has during startup. The maximum torque TH is much lower than the motors peak torque.

In this case the Hydro-flow coupling really behaves as a torque limiter. Moreover, if the machine is jammed, the motors inertia is neutralized automatically.

Depending on the oil level, and the selection of the Hydro-flow coupling, the starting torque may be between 1.2 and 1.5 times the nominal torque, with the delay chamber, and between 1.5 and 2 times without the chamber.

When the machine is jammed, the maximum torque with or without the chamber is twice the nominal torque.

Protective devices

Hydraulic couplings, although different from torque limiters, are safety components capable of protecting the motor and the machine.

Heating of hydraulic couplings directly which in turns depends on the transmitted torque. In case of continuous application of an excessive torque, the coupling’s temperature may exceed that tolerated by the oil, the seals and the bearings.

To prevent this, fusible plugs should be installed. All installed, operation-ready couplings should be fitted with at least one fusible plug.

There are two types of fusible plugs the standard fusible plug and the percussion fusible plug (see Fusible plugs).

In addition to a standard fusible plug, or event an percussion fusible plug, an output speed controller can be installed (see Rotational speed controlled. This equipment monitors the coupling’s temperature by simply reading slippage.

Important: for safety reasons, a protective case must be provided around the coupling. This must incorporate a drip tray with a capacity equal to or greater than that of the coupling.

Drive from the outside

Unless otherwise specified, the Hydro-flow hydrodynamic coupling is delivered for direct installation on the drive shaft (= normal arrangement).

In certain cases, such as complete jamming of the machine or the need to control the coupling manually for filling purposes, it may be useful to reverse installation, i.e. for the coupler to be driven from the outside.

This also allows more effective cooling in operation with repeated overload situations.

Outer rotor B becomes the pump and inner rotor A becomes the turbine. As these two parts do not have identical blade shapes, this should be specified when ordering. Otherwise, the coupling will be delivered for normal arrangement and will not correctly fulfill its purpose as a start-up torque limiter.

A coupling with pulley (HV and HVR) can be driven from the outside if the transmission ratio is 1:1 (call for details). Drive from the outside is prohibited on couplings with a brake disk or drum (H.D and H.B).

For any request for a coupling driven from the outside, add “E” to the code (see Coding).


Hydro-flow coupling, normal arrangement, HP/HPR arrangements

Hydro-flow coupling, driven from the outside, HP/HPR…E arrangements.


Vertical shafts


Under certain conditions, Hydro-flow hydrodynamic couplings can be installed in a position other than horizontal. Correct operation in the vertical position is only guaranteed if the pump is placed in the bottom position, whether drive is from the inside or the outside (see Drive from the outside).


Motor on top and drive from the inside:

Whether used with or without a delay chamber, this position poses no special problem by requires internal arrangements. A version with pulley (HV/HVR) is also offered.

Add “V1” to the code.

Motor on top and drive from the outside:

In this position the delay chamber serves no purpose and the pulley version can be used it the coupler is mounted on the machine shaft.

Add “V2” to the code.

Motor at the bottom and drive from the inside:

This position is only of interest when filling arrangements A to C (see Filling) are suitable, as the pump is located at the top.

A delay chamber serves no purpose. The version with pulley (HV), however, is offered.

Add “V3” to the code.


Motor at the bottom and drive from the outside:

This position is not offered.


An Hydro-flow coupling may be selected in two different ways:

Selection for IEC motors

For each size of IEC motor, the table of the main catalogue section gives the size of the corresponding Hydro-Flow coupling according to the power to transmit and the applicable rotation speed.

For the hollow shaft Hydro-flow couplings (with or without delay chamber) and for the corresponding versions with a delay chamber, the preferred bores Dl are recalled separately in the dimensional drawings and correspond to the diameters of the IEC motors’ shaft ends.

The HV and HVR Hydro-flow couplings are indicated in the table shown on the dimensional drawing, with standard- groove pulleys selected according to the driving powers to transmit.

Selection for other motors or according to the power required

On the diagram below, the input speeds and the powers in kW are shown on the X and Y axes, respectively. The various areas give the field of application for the successive sizes of couplings shown in these areas.


Note: in case of frequent startups or substantial overloads (more than 5 per hour), and for ambient temperatures higher than 40C or for an installation at more than 1000m over see, please consult us for checking the coupling thermal power.


Hydro-flow fluid coupling without delay chamber
Hydro-flow fluid coupling with delay chamber



2 Arrangement code
O: basic arrangement
V: with V-belt pulley
E: with SURE-flex coupling
C: with TEX-O-flex coupling
P: with PENCOflex coupling
T: with HATECO coupling
3 Braking system
without :
 without braking system
B: with brake drum
D: with brake disk
4 Delay chamber
without :
 without chamber
R :
 with delay chamber
5 Size
190,250,280,320,350,400,450,490, 540,620,680,750,870
6 Pulley type
example: 8 SPC 280
Brake disk diameter
315, 355, 395, 625, 705, 795
Brake drum diameter
200, 250, 315, 500, 630
7 Drive and position
None :
 drive from the inside and shafts horizontal
E : drive from the outside and shafts horizontal
V1 : shafts vertical, motor on top and drive from the inside
V2 : shafts vertical, motor on top and drive from the outside
V3 : shafts vertical, motor at the bottom and drive from the inside
8 Protection system
9 Bores and keyways specifications
Without specification, keyways as per ISO R773.


Hydro-flow coupling with PENCOflex coupling, with brake disc and delay chamber, size 620, disk diameter 795 mm, drive from the inside, shafts horizontal, bored hollow shaft to 100 mm, key with reduced height, bored coupling hub to 110 mm with standard keyway as per ISO R773, bore tolerance H7.


The hollow shaft is supplied bored with dimensions L1, LS and S here under:


Size: 190 → 750

Size: 870

D1(G7) 19 24 28 38 42 48 55 60 65 70 75 80 85 90 100 120 135 100 125 130 150
L1 40 50 60 80 110 10 110 140 140 140 140 170 170 170 210 210 240 210 210 265 265
LS 26 34 38 52 74 78 78 98 98 98 98 128 128 120 160 167 167 165 165 187 187
S M6 M8 M10 M12 M16 M16 M20 M20 M20 M20 M20 M20 M20 M24 M24 M24 M24 M24 M24 M36 M36


Brake disk are made in steel and brake drums in cast iron GG 25. As from a 500 mm diameter, the brake drums are made of spherulitic graphite cast iron.

O Basic arrangement
– / R Delay chamber
190 870 Size
– / E / V1 / V2 / V3 Drive & position
V With V-belt pulley
– / R Delay chamber
190 620 Size
Pulley type
– / E / V1 / V2 / V3 Drive & position
E With SURE-flex coupling
– / R Delay chamber
250 620 Size
– / E / V1 / V2 / V3 Drive & position
E With SURE-flex coupling
B With brake drum
– / R Delay chamber
250 620 Size
200 500 Brake drum diameter
– / V1 / V3 Drive & position
E With SURE-flex coupling
D With brake disk
– / R Delay chamber
250 620 Size
315 795 Brake disk diameter
– / V1 / V3 Drive & position
C With TEX-O-flex coupling
– / R Delay chamber
620 87 0 Size
– / E / V1 / V2 / V3 Drive & position
C With TEX-O-flex coupling
B With brake drum
– / R Delay chamber
620 870 Size
500 630 Brake drum diameter
– / V1 / V3 Drive & position
C With TEX-O-flex coupling
D With brake disk
– / R Delay chamber
620 870 Size
705 795 Brake disk diameter
– / V1 / V3 Drive & position
P With PENCOflex coupling
– / R Delay chamber
190 870 Size
– / E / V1 / V2 / V3 Drive & position
P With PENCOflex coupling
B With brake drum
– / R Delay chamber
190 750 Size
200 500 Brake drum diameter
– / V1 / V3 Drive & position
P With PENCOflex coupling
D With brake disk
– / R Delay chamber
190 750 Size
315 795 Brake disk diameter
– / V1 / V3 Drive & position
T With HATECO coupling
– / R Delay chamber
190 620 Size
– / E Drive & position

Fusible plugs

Standard fusible plug

Unless otherwise specified, this plug consists of a core made of a material which melts at a temperature of +145C. A different melting temperature can be supplied on request. The figure below defines the marking system of the plugs, according to melting temperature.

Note: A plug with a fuse temperature of 200C is possible but not recommended.

When the oil temperature exceeds that of the plug, the fusible core melts and the oil is drained out of the coupling. Torque transmission is then stopped and the machine is no longer driven. The motor is no longer overloaded and undamaged.

Important: for safety reasons, a protective case must be provided around the coupling. This must incorporate a drip tray with a capacity equal to or greater than that of the coupling.

Percussion fusible plug

This plug comprises a striker retained by a material melting at +120C. A temperature of +140C can be obtained on request.

When the oil temperature exceeds that of the percussion fusible plug, the material melts and releases the striker.

The striker then breaks a glass bulb which opens an electrical contact. This contact is available to the user to cut off the power supply to the motor and/or trigger an alarm, for example. (see Thermal protection below)

This plug avoids draining the oil in case of excessive torque.

Important: the percussion fuse plug should under no circumstances be installed without a standard fusible plug.


Percussion fusible plug


Thermal protection


Size H D1
G1 G2 D1
G3 G4 D1-D2
G1 G2
190 266 28 63 58 2xSPA 106 28 90 95 40 133 128
250 288 42 72 83 3xSPA 132 42 140 129 55 160 171
280 300 48 69 91 4xSPA 132 48 152 130 55 157 179
320 319 48 65 97 4xSPA 150 48 158 126 70 165 197
350 338 55 68 119 5xSPB 180 55 214 162 85 197 248
400 361 65 76 142 6xSPB 200 65 257 191 85 203 269
450 384 85 83 162 6xSPC 236 85 310 231 100 224 303
490 403 85 63 154 8xSPC 236 85 353 262 100 204 295
540 424 90 94 195 4xSPC 280 80 284 183 120 259 360
  424 100 129 230 8xSPC 280 100 386 285
620 461 90 199 4xSPC 280 80 288 120 364
  461 100 234 8xSPC 280 100 390
680 426 120 186
750 464 135 204
870 527 150 236


Example of wiring
(**): our supply


D512-1: Electric contact IP66 with gland, base and glass fuse.

Speed controller


As the transmitted torque is increased, this gives rise to an increased slip of the hydrodynamic coupling, and consequently, a decrease of the coupling case speed. It is therefore possible to detect this increase of the resisting torque (overload) of a Hydro-flow coupling driven from the inside, using an electronic rotational speed controller which measures its speed.

A relay with change-over contact at the output may either emit an alarm signal or switch off the main motor.

A delaying action of maximum 60 s prevents the unnecessary triggering of the relay, when the motor is started. It only occurs once when the operating voltage is applied.

False alarms are prevented arising from I very short torque fluctuations, by the introduction of a preset time lag of 5 s.


Speed controller
Supply: 230V AC – 24V DC

Time delay relay
Supply: 230V AC


– Speed controller
Turn 1 to the minimum setting, 3 at 1, 4 at 100, 5 at 1.
– Time delay relay:
Set a at 10, b at 0,1m.

Control adjustment – preset
1. Required switching point e.g. 1300 min-l.
2. Two pulse initiators:
1300 x 2 = 2600 p/min. 2 at 26.

Accurate setting on the machine
1. Should the main motor be switched off by the speed controller, the subject relay contact has to be bypassed.
2. Turn 2 completely to the right.
3. Make sure the max. allowable absorbed power of the machine is reached.
4. After about 60 s LED will light on.
5. Turn 2 slowly to the left until LED is off again.
6. Reset the controller : 4 to 1 and back to 100.
7. If after 5 a LED lights on again repeat from 5.

(*) : Bore Dl = 100 mm


Size B A

190 117 100 2xSPA 130 170
250 149 95 3xSPA 155 185
280 165 100 4xSPA 165 190
320 187 100 4xSPA 165 200
350 201 110 5xSPB 205 238
400 231 127 6xSPB 242 253
450 261 138 6xSPC 286 278
490 284 127 8xSPC 326 267
540 311 170 4xSPC 260 335
311 8xSPC 360
620 357 160 4xSPC 250 325
357 195* 8xSPC 350
680 389 167
750 429 185
870 496 215


Example of wiring
(**) : our supply


D100: Speed controller
D100-PT: Pulse transmitter
D100-K2: Time delay relay


Couplings in the as-delivered state The Hydro-flow couplings are delivered without oil.

They are equipped with sealing rings capable of withstanding a continuous duty temperature of up to +90’C. For higher temperature, use special rings. Call for details.


A protective cover encasing the coupling shall be provided to preclude any oil projections. The cover shall not impair cooling. The cover shall incorporate a drip tray with a capacity equal to or greater than that of the coupling. Case of the hollow shaft coupling mount the Hydro-flow coupling on the shaft using a threaded rod screwed in the shaft tapped hole, a spacing ring and a nut. To prevent the shaft from rotating, use a nut with a cheek-nut attached to the threaded rod, held by a second wrench.

Remove the rod from the shaft and lock the coupling using a screw and a washer. When the coupling is installed on a motor shaft, use the motor’s inertia to unscrew the threaded rod and screw the axial attaching screw.

For installation of the coupling parts of couplings types HE, HC, HP, HT, see the instructions relating to couplings SURE-flex, TEX-0-flex, PENCOflex and HATECO, respectively.


Maintenance of Hydro-flow couplings is limited to changing the oil every 8000 hours or once a year.

As regards the coupling parts of couplings types HE, HC, HP and HT, see the instructions relating to couplings SURE-flex, TEX-0-flex, PENO0flex and HATECO, respectively.


Screw a threaded rod with a diameter as indicated in table below and extract the coupling. The threaded rod can be supplied on request.


Size M
190 1/2 – 20 UNF
250 – 320 M20
350 – 400 R 1″
450 – 620 R 11/4″
680 – 870 M45



Align taking care to comply with the instructions of page 12 and the maximum Δ values below.





Type Size 190 250 280 320 350 400 450 490 540 620 680 750 870
HE & HER EΔE 330+2 400+2 400+2 460+2,5 530+2,5 640+2,5 730+3 880+3 880+3
(b-a) 2,4 2,8 2,8 3,3 3,8 4,5 5,0 6,2 6,2
Δr 0,5 0,6 0,6 0,6 0,8 0,8 1,0 1,2 1,2
HC & HCR EΔE 90+2 90+2 110+2 110+2
(b-a) 2,2 2,4 2,8 2,8
Δr 1,0 1,0 1,2 1,2
HP & HPR EΔE 3,50+2 3,50+2 3,50+2 3,50+1,5 3,50+1,5 3,50+1,5 40+2 40+2 40+2 40+2 40+2 40+2 5,50+2,5
(b-a) 0,30 0,30 0,30 0,30 0,30 0,30 0,45 0,45 0,45 0,45 0,45 0,45 0,60
Δr 0,2 0,2 0,2 0,2 0,2 0,2 0,3 0,3 0,3 0,3 0,3 0,3 0,3


1620,5 214,50,5 223,50,5 226,50,5 2850,5 3070,5 3260,5 3260,5 3820,5 5820,5


3450,5 3750,5 4060,5 4060,5 4820,5 4820,5
Δa 3 3 3 3 3 3 3 3 3 3
Δr 0,4 0,4 0,4 0,4 0,4 0,4 0,6 0,6 0,6 0,6



HTR 620



Use an oil with a viscosity VG 1 5, VG22 or VG32 to standard ISO 3448.

Remove the two fusible plugs acting as filling plugs and pour the oil quantity stated in the table below according to the coupling size. The letters in the table correspond to the coupling markings. Turn the coupling until the adequate marking is at the top point and fill the coupling until the oil reaches the filling port level.

For optimum operation (minimum slip and start-up torque), determine the oil quantity as a function of the input power. The values not given in the table are calculated by interpolation. Increasing the oil quantity reduces slip but the peak torque to rated torque ratio will increase. The reverse occurs when reducing the oil quantity. A high slip reduces the coupler efficiency and increases the oil temperature.

Refit the plugs. As these plugs have tapered threads, sealing is provided by tightening. A mounting compound can be used for easier installation.




Size Oil Quantity (Liter)
190 0,92 0,86 0,80 0,73 0,65
250 1,95 1,80 1,70 1,55 1,40
280 2,75 2,55 2,35 2,10 1,85
320 4,10 3,80 3,50 3,20 2,90
350 5,20 4,80 4,40 4,00 3,60
R350 7,50 7,00 6,30 5,70 5,10
400 7,60 7,10 6,60 6,00 5,40
R400 9,90 9,50 8,90 7,70 6,30
450 11,50 11,00 10,00 9,00 8,00
R450 15,90 14,40 13,60 12,90 11,70
490 14,00 13,50 12,50 11,00 10,00
R490 18,90 17,80 15,90 15,10 14,00
540 19,00 18,00 16,50 15,50 13,50
R540 27,60 25,40 23,50 21,90 19,70
620 28,50 26,50 24,50 22,50 20,50
R620 37,50 34,50 31,50 28,80 26,10
R680 57,00 53,00 50,00 46,50 43,00
R750 72,00 68,50 63,00 59,00 54,00
R870 107,00 100,00 92,50 88,50 83,50