How manufacturers choose hydraulic oil and flow meter

In the fields of industrial automation and mechanical transmission, hydraulic systems, with their high power density and precise control capabilities, have become the core power source for heavy machinery, construction machinery, aerospace, and other fields. Hydraulic oil, the "blood" of a hydraulic system, directly determines its operating efficiency and service life through its performance and flow monitoring. Flowmeters, key instruments for hydraulic oil monitoring, are closely linked to the manufacturer's technical expertise. This article will begin with a basic understanding of hydraulic oil, delve into key hydraulic oil parameters and applicable flowmeter types, and systematically review major domestic and international flowmeter manufacturers and their recommended products, providing a comprehensive reference for industry practitioners.
1. Hydraulic Oil as the "Powerful Blood" of the Hydraulic System
Hydraulic oil, or hydraulic fluid, is the medium that transmits power in hydraulic machinery. Common hydraulic oils are based on mineral oil or water. Equipment that may use hydraulic oil includes excavators and backhoes, hydraulic brakes, power steering systems, automatic transmissions, garbage trucks, aircraft flight control systems, elevators, and industrial machinery.
Hydraulic oil is a specialized lubricant that transmits energy, lubricates components, cools equipment, and prevents corrosion within a hydraulic system. It not only needs to have good fluidity to ensure efficient energy transfer, but also needs to maintain stable performance under harsh working conditions such as high temperature, high pressure, and high load to avoid system failure due to oil deterioration. From the perspective of functional classification, hydraulic oil mainly includes three categories: mineral oil hydraulic oil, synthetic hydraulic oil and biodegradable hydraulic oil: mineral oil hydraulic oil is widely used in ordinary industrial scenes due to its low cost and strong compatibility; synthetic hydraulic oil is suitable for high-end fields such as aerospace and metallurgy due to its high temperature resistance and good flame retardancy; biodegradable hydraulic oil is targeted at scenes such as engineering machinery and agricultural machinery with high environmental protection requirements, which can effectively reduce environmental pollution. (1) Core technical parameters of hydraulic oil The performance of hydraulic oil is reflected by a series of key parameters, which are also an important basis for flow meter selection. Among them, viscosity is one of the most core parameters of hydraulic oil, which directly affects the fluidity and energy transfer efficiency of the oil. Typically, the viscosity of hydraulic oil is selected based on the system's operating temperature. Low-viscosity oils (such as ISO VG 32) are used in low-temperature environments to prevent cold-start difficulties, while high-viscosity oils (such as ISO VG 100) are required in high-temperature environments to prevent excessive dilution and leakage. Furthermore, the viscosity index (VI) is crucial. Hydraulic oils with a high viscosity index (e.g., VI 140) exhibit minimal viscosity fluctuations with temperature changes, allowing them to operate over a wide temperature range.
a. Viscosity
Common hydraulic oil viscosities are classified using the ISO VG (viscosity grade) system, which is based on the oil's kinematic viscosity at 40°C (104°F). The most common viscosity grades for general industrial and mobile hydraulic systems are:
- ISO VG 32
- ISO VG 46
- ISO VG 68
Additional viscosities are also used, but are less common or reserved for specific low- and high-temperature applications. - ISO VG 15
- ISO VG 22
- ISO VG 100
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b. Flash point and fire point
These are key indicators of hydraulic fluid safety. The flash point refers to the lowest temperature at which flammable vapors are produced when heated under specified conditions, while the fire point is the lowest temperature at which these vapors continue to burn. For applications involving high temperatures or the risk of open flames (such as metallurgical machinery), hydraulic fluids with high flash points should be selected to reduce fire hazards. Oxidation stability determines the service life of hydraulic fluids. High-quality hydraulic fluids are less susceptible to oxidation and deterioration under long-term high-temperature and high-pressure conditions, reducing the formation of impurities such as sludge and carbon deposits and extending oil change intervals. Furthermore, parameters such as anti-wear properties, rust resistance, and demulsibility should also be considered based on system requirements. For example, high-pressure hydraulic systems require hydraulic fluids with excellent anti-wear properties to protect precision components such as pumps and valves. For humid environments, the demulsibility of the hydraulic fluid should be of particular concern to prevent moisture intrusion and the resulting emulsification failure of the oil. 2. Hydraulic oil flow meter: the "core equipment" for precise monitoring Hydraulic oil flow monitoring is a key link to ensure the stable operation of the hydraulic system. By monitoring the hydraulic oil flow in real time, problems such as system leakage and pump valve failure can be discovered in time, avoiding equipment damage or production accidents caused by abnormal flow. According to the measurement principle and structural characteristics, the flow meters suitable for hydraulic oil are mainly divided into the following categories: (1) Volumetric flow meter: the "preferred solution" for high-viscosity oils Volumetric flow meter calculates the flow rate by measuring the number of times the hydraulic oil is filled and discharged in a fixed volume cavity. It has the characteristics of high accuracy and strong viscosity adaptability, and is particularly suitable for measuring high-viscosity hydraulic oil (viscosity 100 cSt). Among them, the oval gear flow meter is the mainstream product for hydraulic oil measurement - it consists of two meshing oval gears. When the hydraulic oil drives the gear to rotate, a fixed volume of oil is discharged for each rotation. The flow rate can be obtained by counting the number of gear rotations. The accuracy of this type of flowmeter can usually reach level 0.5, and some high-end products can even reach level 0.2. It is less affected by fluid viscosity and temperature changes and is widely used in scenarios such as oil quantity measurement and leak detection in hydraulic systems. (2) Turbine flowmeter: "Efficient choice" for medium and low viscosity oils The turbine flowmeter uses hydraulic oil to drive the turbine to rotate, and uses the principle of electromagnetic induction to convert the turbine speed into an electrical signal to calculate the flow rate. It has the advantages of fast response speed and wide measuring range, and is suitable for dynamic flow monitoring of medium and low viscosity hydraulic oil (viscosity <50 cSt), such as real-time flow control of hydraulic systems, flow regulation when equipment load changes, and other scenarios. The accuracy of turbine flowmeters is usually level 0.5-1.0. Some products can achieve level 0.2 accuracy by optimizing the turbine structure and signal processing technology. However, it should be noted that turbine flowmeters have high requirements for fluid cleanliness. If there are impurities in the hydraulic oil, it is easy to cause the turbine to jam or wear, affecting the measurement accuracy and service life. (3) Other types of flow meters: "supplementary solutions" for special scenarios
In addition to volumetric and turbine flow meters, ultrasonic flow meters and electromagnetic flow meters are also used in some special scenarios. Ultrasonic flow meters calculate flow by measuring the propagation time difference of ultrasonic waves in hydraulic oil. They have the advantages of non-contact measurement and no pressure loss. They are suitable for measuring large-caliber, high-viscosity hydraulic oils, but are easily affected by bubbles and impurities in the oil. The accuracy is relatively low (usually 1.0-2.0 level). Electromagnetic flow meters use the principle of electromagnetic induction to measure the flow of conductive liquids. However, if the conductivity of the hydraulic oil is low, they will not work properly. Therefore, they are only suitable for synthetic hydraulic oils or water-containing hydraulic oils with high conductivity.
3. Mainstream hydraulic oil flow meter manufacturers and recommended products at home and abroad
The performance of hydraulic oil flow meters is closely related to the manufacturer's technical accumulation and production process. A number of companies specializing in flow measurement have emerged at home and abroad. They have become benchmarks in the industry with their advanced technology and reliable products. (1) Domestic manufacturers: representatives of high cost performance and customized services
a. Anhui JUJEA Instrument Co., Ltd.
As a leading enterprise in liquid flowmeters, Anhui JUJEA Automation Technology Co., Ltd. has been deeply engaged in the field of hydraulic oil flow measurement for many years. Its core product, the GT-LC series oval gear flowmeter, is a "weapon" for measuring high-viscosity hydraulic oil. This series of flowmeters is made of high-quality stainless steel, which is resistant to high pressure and corrosion. It can adapt to the working temperature of up to -20℃-200℃, and perfectly matches the harsh working conditions of the hydraulic system. In terms of accuracy, the basic error of the GT-LC series flowmeter is ≤±0.5%. Some models can improve the accuracy to ±0.2% by optimizing the gear processing technology and signal acquisition technology, far exceeding the industry average. In addition, this series of flowmeters also supports multiple output modes (pulse output, 4-20mA current output), and can be seamlessly connected with control systems such as PLC to achieve real-time transmission and remote monitoring of flow data. In response to the needs of different users, Anhui JUJEA also provides customized services, such as designing high-pressure resistant housings for high-pressure hydraulic systems and optimizing oil viscosity compensation algorithms for low-temperature environments to fully meet personalized application scenarios. b. Everud Fluid Technology (Shanghai) Co., Ltd. (Part of the German E.HOLDING Group)
Everud Fluid Technology (Shanghai) Co., Ltd., a wholly-owned subsidiary of the German E.HOLDING Group in China, leverages the core R&D achievements and manufacturing processes of VSE Flowmeter Technology Co., Ltd., a subsidiary of the group, to establish itself as an industry benchmark in high-end hydraulic oil flowmeters. The VSE brand's VS series oval gear flowmeters, with their superior measurement accuracy and long-term stable performance, have become the preferred choice for precision flow monitoring in numerous hydraulic systems.
This series of flowmeters features a unique gear meshing mechanism. This design carefully considers the flow characteristics of the fluid within the measuring chamber, minimizing fluid disturbances during flow. This ensures stable and accurate measurement even in low-flow hydraulic system conditions, effectively avoiding measurement deviations commonly encountered in these conditions.
Thanks to its outstanding performance, the VS series oval gear flowmeters are widely used in applications requiring the highest levels of accuracy and stability. In the aerospace field, it can be used to monitor flow in spacecraft hydraulic control systems, ensuring precise operation in complex space environments or high-altitude conditions. In high-end equipment manufacturing, such as in the hydraulic systems of precision machine tools and large industrial robots, it can also provide reliable flow data to support stable equipment operation, making it suitable for a variety of demanding industrial applications.
C. Emerson Process Management (Emerson)
As a global leader in industrial automation, Emerson Process Management has introduced the Micro Motion series of Coriolis mass flowmeters, bringing innovative solutions to the hydraulic oil flow measurement industry.
Coriolis mass flowmeters are based on a unique Coriolis force measurement principle. They directly measure fluid mass flow by sensing the force effects generated by fluid flow within a specifically designed pipe. This measurement method fundamentally eliminates the traditional flowmeter's reliance on the fluid's physical properties. Changes in hydraulic oil viscosity, operating temperature fluctuations, and system pressure adjustments remain unaffected, ensuring accurate measurement results. Therefore, it is recognized in the industry as the "gold standard" for hydraulic oil mass flow measurement.
In practical applications, this series of flowmeters has demonstrated exceptional practicality. During the construction machinery manufacturing process, it precisely controls hydraulic oil filling operations, ensuring consistent hydraulic oil levels for every piece of equipment shipped. This ensures consistent quality and reduces performance variations caused by oil quantity variations. During routine hydraulic system maintenance, real-time monitoring of oil loss provides maintenance personnel with accurate oil consumption data, enabling the development of scientific and rational maintenance plans and preventing equipment failures caused by insufficient or excessive oil consumption.

4. Flowmeter Manufacturer Selection Recommendations and Industry Trends
(I) Key Selection Principles from a Manufacturer's Perspective

Based on the practical experience of flowmeter manufacturers, the selection of hydraulic oil flowmeters must adhere to the three key principles of "suitability for operating conditions, matching accuracy, and cost control." First, the appropriate flowmeter type must be selected based on hydraulic oil viscosity, temperature, and pressure. For high-viscosity hydraulic oil, an oval gear flowmeter is preferred, while for medium- and low-viscosity hydraulic oils, a turbine flowmeter can be used. For high-temperature and high-pressure applications, the flowmeter's material and sealing performance should be considered. Secondly, accuracy requirements must match the application scenario. For general industrial applications, a Class 0.5 accuracy level is sufficient, while for high-end equipment manufacturing, metrology, and calibration, products with Class 0.2 accuracy or higher are required. Finally, equipment and operating costs must be carefully considered to avoid excessive pursuit of high accuracy that results in wasted costs.
(II) Industry Development Trends in Hydraulic Oil Flow Meters
With the advancement of Industry 4.0 and smart manufacturing, hydraulic oil flow meters are moving toward "intelligence, integration, and greening." In terms of intelligence, manufacturers are equipping flow meters with smart sensors and wireless communication capabilities. In terms of integration, integrated flow measurement modules are becoming a trend. For example, VSE's integrated flow meter, designed for multi-channel hydraulic systems, can simultaneously measure flow in multiple oil circuits, reducing equipment size and installation costs. In terms of greening, manufacturers are reducing flow meter energy consumption and environmental pollution by optimizing product structure and selecting environmentally friendly materials.