In the 1990s, traditional nuts could no longer meet the fastening requirements of many heavy machinery fields. At this time, a new type of powerful fastening element, hydraulic nut, appeared. A hydraulic nut is not a precise mechanical part. In simple terms, it is an ordinary machine part made of iron and steel. It is often used for bolt pre-tightening of mechanical parts, and can also lock some mechanical workpieces. So, do you know how hydraulic nuts work? In fact, the working principle of the hydraulic nut is mainly to complete the installation or removal of the shaft through the piston thrust generated by the high-pressure oil pump pushing the hydraulic oil into the nut. The use of hydraulic nuts greatly reduces the time required for work.

Introduction to Hydraulic Nuts

Hydraulic nut is a detachable tool that is often used on relatively large machines to lock the interface, generally in a circular or conical shape. This is very suitable for the use of specific workpieces, which can be installed and removed easily.

Features of Hydraulic Nuts

1. The stretching method is not affected by the lubricating effect of the bolt and the friction of the thread, and a more accurate bolt load can be obtained;

2. Multiple bolts can be stretched synchronously so that the whole circle of bolts is evenly stressed and a balanced load is obtained;

3. Due to the use of the most advanced ultra-high pressure hydraulic technology, the bolt locking can be completed in a small space;

4. The residual load and effective load obtained when the bolt is tightened by the tension method are larger than those obtained by the torque method;

5. The stretching method is more suitable for joining applications that require higher fastening accuracy. It can make the joint face evenly forced to achieve joint, and truly prevent leakage.

Advantages of Hydraulic Nuts

1. Suitable for all kinds of vibration, rapid rotation, high-power equipment and narrow spaces;

2. Economical and efficient, lightweight and high precision;

3. It can be equipped with manual hydraulic pump, pneumatic hydraulic pump and electric hydraulic pump;

4. Multiple hydraulic nuts can be used at the same time;

5. There is no need to use a gauge, and the measuring ring in the structural design can directly and accurately measure the axial approach distance required by the bearing;

6. When installing and disassembling the withdrawal sleeve, the hydraulic nut of the same specification can be used, which can not be realized by other patented hydraulic nuts with gauges or hanging blocks cannot have;

7. Use the additional screws of the measuring ring to decompose the nut to replace the damaged O-ring, which saves time and parts cost compared with the general design;

8. Sealed bearings can be installed, and there is no need to measure the internal clearance of the bearing to determine the axial thrust of the bearing.

The Working Principle of Hydraulic Nut:

Hydraulic nut is an advanced bolt tightening system with the same working principle as hydraulic tensioner. It is mainly used for fastener assembly in narrow spaces and the tightening of heavy-duty vibration machinery. It reforms the traditional tightening method, using the hydraulic system to make the tightened bolt through pure axial tension, accurately reaching the predetermined load, and then mechanically locking it on the fastener to complete the tightening work. Since the screw is only subjected to pure tensile force, the pre-tightening force of the bolt pair can be increased by 20%-30%.

Hydraulic nut is an advanced bolt assembly method, especially suitable for the tightening of narrow spaces and heavy-duty vibration machinery. The working principle of the hydraulic nut is to use the hydraulic cylinder to directly apply an external force to the bolt so that the bolt to which the force is applied is elongated in its elastic deformation zone. After the bolt is elongated, tighten the lock ring on the hydraulic nut, so that the bolt will be locked. The loop locks in the elongated position.

The hydraulic cylinder is located at the position of the central axis of the bolt, which is used to stretch the bolt axially to achieve the required stretching amount of the bolt. And it is this amount of tension in the bolt that determines the clamping force required for bolt tightening. When the hydraulic nut is pressurized, the bolt is stretched, and at the same time, the hydraulic nut and the joint surface are close to each other, thereby locking the axial deformation of the bolt, that is, locking the remaining bolt load in the nut. There are gaskets between many connecting surfaces. The gaskets only work when the connecting surfaces are pressed, so it is especially important that the connecting surfaces are always clamped. The load applied to the bolt is proportional to the oil pressure in the hydraulic cylinder, which is designed to retain the payload very precisely. Since the load is applied directly to the bolt and all forces are used to elongate the bolt, the space required for load generation can be minimized.

Hydraulic Nut Application

1. Hydraulic nuts are widely used in metallurgical copper and aluminum metal industry, paper industry, hydraulic locking on slitting machines, etc.;

2. Installation and removal of propellers, rudder pads, etc.;

3. Remove the high-voltage connection table, such as train wheels, couplings, flywheels and gears.

Hydraulic nuts can not only be used alone or in combination but also can be equipped with manual or pneumatic and electric hydraulic pumps. It’s a good way to measure distance without using a scale when in use. Hydraulic nuts are widely used in some papermaking industries and some metallurgical industries. Hydraulic nuts can be used to install or unload some propellers and rudder pads, and can also be used to disassemble the connection table of train wheels and flywheels.

Hydraulic Nut Installation

1. Prepare the hydraulic nut, screw it into the workpiece, lock the nut after connecting, and pay attention to fixing the pressure ring of the hydraulic nut in the original place.

2. Insert the oil filling port of the manual pump into the oil filling port of the hydraulic nut, and lock the unloading switch handle on the right side of the manual pump, then slowly pressurize it and release the air release cap above the oil drain joint, until the air inside the nut is expelled.

3. After the air in the nut is released, rotate the air cap outwards, close the one-way valve, and then pressurize the oil to press the pressure ring of the hydraulic nut outward. When the pressure is required to be pressed, loosen the handle of the unloading switch, and loosen the pressure joint of the manual pump, and the installation can be completed.

Precautions for the Use of Hydraulic Nuts

1. When using hydraulic nuts, we should pay attention to the delivery volume of hydraulic oil. The delivery volume of hydraulic oil is related to the actual use of our hydraulic nut, so we should pay close attention to its situation;

2. When using hydraulic nuts, we should pay attention to the connection of the interface when combining them with large workpieces, which is related to the safety of our use of hydraulic nuts. If it is not connected well, there will be many problems, such as waste of hydraulic oil, waste of time, and most importantly, safety issues;

3. After using the hydraulic nut, we should clean the hydraulic nut in time.


The above is the introduction of the working principle of hydraulic nut, the use of hydraulic nut and the precautions. Due to the research on hydraulic technology, the hydraulic nut can lock the bolt in a narrow space and minimize the load space. We can also use hydraulic nuts to stretch multiple bolts together, so that the force is even, so as to achieve a balanced load.