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As we all know, scientific research aims to answer “why,” while technological R&D aims to solve “how to do it to meet human needs.” Therefore, hydraulics exists to meet human needs. Hydraulic drives need to limit pressure, flow, and flow direction, and valves serve this purpose.
Over more than two hundred years, hydraulic technology has been widely applied, and different applications have put forward different performance requirements for valves. For example, they need to adapt to different working environments, such as severe cold, extreme heat, sun and rain exposure; some need to be corrosion-resistant, some need to be explosion-proof. For mobile hydraulics, small size and light weight are often desired. Industrial and agricultural applications differ, grassland and desert applications differ, metallurgical and mining applications differ, iron ore and coal mine applications differ, and underground and above-ground coal mine applications also differ. Those used in hospitals and offices not only require no leakage but also expect no odor, and so on.
In a market economy environment, whether Eastern valve or Western valve, one that meets application requirements is a good valve; whether domestic or imported, only those that meet application requirements are good valves.
Different applications may have different priorities for requirements, and the order of concern also differs. Therefore, comprehensive, in-depth, and detailed research on requirements is necessary.
Application requirements for hydraulic valves can generally be summarized in the following aspects:
(1) Control Performance: Fine adjustment capability, including but not limited to high stability and repeatability. One must clearly recognize that function ≠ performance! Function refers to what it can do; while performance refers to how well it does it, whether it’s good or not! Over more than two hundred years of hydraulic valve application, predecessors have invented many peculiar structures. Following them can basically achieve corresponding functions, but cannot guarantee excellent performance. Not only steady-state performance, but more difficult is transient performance. This is the main battleground for valve performance competition, see details in Sections 4.9 and 4.10. The control performance of valves involves many design, processing, and assembly details. It is achieved through trial and improvement, measured through testing, must be backed by data, and there is only better, no best!
(2) Pressure Resistance: Modern hydraulic systems have large working pressure fluctuations and often experience very high instantaneous pressure shocks. Hydraulic valves must be able to withstand them. Therefore, during R&D, pressure resistance tests of at least 125% of the rated pressure must be conducted. At high pressure, the performance of hydraulic valves may differ from normal working pressure, which is still acceptable. The important thing is that after the high pressure disappears, the control performance remains normal! Therefore, after conducting pressure resistance tests, performance testing under normal working conditions should be conducted again.
(3) Durability: Most application scenarios expect hydraulic valves to work durably (long lifespan). Advanced enterprises are using new materials and new processes to improve the working durability of hydraulic valves.
Of course, durability requirements are not absolute. Some equipment works day and night, while some equipment moves only once every few days, months, or even years. Oceangoing ships and wind turbines expect hydraulic valves to work for 20 years, while hydraulic valves on missiles only need to work for tens of minutes. Generally speaking, what affects the durability of mechanical parts is mainly wear. Therefore, durability is a main indicator for measuring pumps. Because the speed at which valve spools move is much slower than those friction parts in pumps, and the normal pressure on friction surfaces is also much smaller, compared to pumps, valve durability is relatively easy to meet application requirements and is not a difficulty.
(4) Product Stability: Not only one is good, but all must be good, that is, the consistency of product performance must be guaranteed, commonly measured in PPM. That is, out of one million possible defects, how many defects appear. This is particularly important for mass-production OEMs, such as automobile, excavator, and loader manufacturers.
Absolute absence of defects is impossible to achieve. It’s better to first honestly and objectively inspect and count current defects, then find causes and study how to reduce them. With perseverance, the defect rate can be reduced from 0.1% to 0.01% or even lower.
How can stable manufacturing quality be obtained? Relying solely on factory inspection is far from enough, and relying on fines and wage deductions cannot achieve high standards!
According to references, LiuGong once sent management personnel to Caterpillar in the United States to study in 1986. Once, a LiuGong manager asked a Caterpillar trainer: “If quality problems are found on the production floor, how do you handle the operator?” The Caterpillar trainer, departing from his usually gentle tone, said very sternly: “This is a stupid question. Our quality management is first and foremost the responsibility of management, and only then the responsibility of operators. When quality problems occur, we must first see whether the process flow formulated by managers is correct and whether operator training is adequate, not punish operators. If problems are found, managers should be punished first.”
European and American manufacturers generally believe that stable manufacturing quality must be obtained through management and following certain processes, which is why there is ISO 9001.
The International Automotive Task Force (IATF) and members of ISO/TC 176 together, in 1999, added special requirements for the automotive parts industry based on ISO 9001 and wrote the first edition of the ISO/TS 16949 “Quality Management System” standard as requirements for suppliers. Some advanced hydraulic component manufacturers have already begun implementation. The current version is IATF 16949:2016. This standard requires enterprises to implement the following five core tools: 1) Advanced Product Quality Planning and Control Plan APQP. 2) Production Part Approval Process PPAP. 3) Failure Mode and Effects Analysis FMEA. 4) Measurement System Analysis MSA. 5) Statistical Process Control SPC. Some Chinese hydraulic component manufacturing enterprises, especially those doing OEM work for international brands, have now begun to inspect and improve product quality control processes according to Germany’s “Automotive Industry Process for Supplier Assessment and Classification Management (VDA 6.3).”
However, for projects with very small batches, even just one product at a time, where on-site product debugging is allowed, the requirement for product performance consistency is not high. Having greater flexibility and adjustability is itself a very prominent advantage of hydraulic technology.
(5) Reliability: Theoretically defined as: capable of completing specified functions within specified time under specified conditions.
For hydraulic valves, high reliability means: 1) The performance of individual valves must meet requirements. Because hydraulic valves wear during operation, their performance must meet requirements not only at the beginning of use but also after long-term operation. 2) Because mechanical manufacturing always has deviations and cannot be absolutely problem-free, a more realistic requirement is to expect very few valves that fail to meet requirements, for example, less than 100 out of one million, or even less than 10.
Therefore, for hydraulic valves, in practice, reliability is a comprehensive reflection of excellent design performance and stable manufacturing quality.
Because if one component in a hydraulic system fails, it may affect the normal operation of the entire system and equipment. Replacing failed components not only means spending money to purchase replacement parts and pay for repairs, but also often means that the entire equipment must be temporarily shut down, and this loss often exceeds the cost of replacement parts and repairs. This is why in many situations, users are willing to pay higher fees to purchase more reliable components.
Since entering the 21st century, internationally, “Mean Time To dangerous Failure (MTTFd)” (or “Mean Time To Failure MTTF”) has begun to be used to measure the reliability of hydraulic valves. This is an indicator obtained by sampling from products that have passed factory inspection and conducting durability tests simulating actual working conditions. Working continuously for one full year, if the probability of dangerous failure is < 3.3%, it can be said that MTTFd > 30 years; only if the probability of dangerous failure is < 0.6% can it be said that MTTFd > 150 years. Hydraulic valves at the world’s advanced level have reached this level.
These requirements for hydraulic components are benchmarks for measuring hydraulic valve standards and dividing hydraulic valve grades.
Of course, so-called excellence is also relative; there is no absolute excellence. Being more suitable for application requirements than competitors’ products is good.
(6) Market-Appropriate Pricing: In the modern market economy environment, all commodities must be priced. It’s just that some markets have stronger demands for low prices, while some pay more attention to reliability.
The hydraulic valve market can be divided into front market and aftermarket, with different requirements. 1) Front market: Providing valves to OEMs according to their requirements, commonly called “doing OEM.” Generally, after valves are officially accepted by OEMs, order quantities per batch are larger, but requirements for performance consistency and service life (warranty period of at least one year) are stronger, and payment terms are often quite tough, especially for some first-tier manufacturers. Supply and demand relationships are relatively fixed, so after-sales service quality also becomes an important evaluation indicator. 2) Aftermarket: Providing replacement parts.
Although the aftermarket may have lower requirements for performance consistency, service life (warranty period of more than three months), and low price, batches are often small and varieties diverse.
Of course, different customers and different applications have different price affordability.
Cost-performance ratio is a very sensitive factor and plays an extremely important role in industrial development, yet it is a pseudo-indicator that’s easy to discuss but difficult to calculate. Because price can still be expressed in numbers, but performance involves multiple factors and is difficult to comprehensively express in numbers.
In fact, the prices of most domestic hydraulic components are undervalued relative to their importance to main machines. One piece of evidence is that some imported hydraulic components are much more expensive than domestic ones, yet OEMs can afford them.
One reason is that hydraulic valve manufacturing mostly doesn’t require qualifications and is relatively easy to start: a few people investing a few hundred thousand yuan, purchasing some machinery and equipment, can make some hydraulic valves. For some domestic hydraulic valve manufacturers, because they reverse-engineer and imitate, they don’t need much R&D cost and can press prices extremely low for market competition—cheap, rolling! As a result, domestic hydraulic component prices are pressed to very low levels. Low selling prices mean insufficient profit to provide good after-sales service and support R&D, leading to a vicious cycle.
Some hydraulic valves were originally not produced in China. European, American, and Japanese products came first and are relatively more reliable than domestic latecomers, with better reputations. Because hydraulic technology is already very mature, identifying and judging hydraulic component quality requires considerable technical level and considerable time, so some OEM procurement personnel take shortcuts: Anyway, I imported the most expensive hydraulic components; if any problems occur, I have no responsibility!
Relative pricing has a great impact on how fast products open up markets.
Cost is the foundation of price. What valve manufacturers can pursue is: how to manufacture products with high yield, high efficiency, and low cost while ensuring product performance meets requirements! For example, decomposing processes, simplifying each process operation, organizing assembly line production well, improving production efficiency, and gradually automating production lines.
Reputation alone cannot rely on self-promotion; it also needs market recognition, so user feedback must be carefully attended to and seriously handled.
Great effort must be spent studying customer application requirements and continuously improving. At the same time, there must be technically knowledgeable sales personnel, or application engineers. Sales personnel need to know more and deeper than customers, knowing what valves are appropriate for customers’ applications, able to convince and satisfy customers.
Of course, there is no absolute satisfaction, but the more satisfied the better! Being more satisfying than others—competitors—meeting user needs better, with better performance and lower prices, means stronger competitiveness.
In terms of function, hydraulic valves are universal components that can be used in various industries and occasions. But if one thinks that there’s no need to visit customers and understand customer needs, and just wait for customers to come—like Jiang Taigong fishing, waiting for the willing to take the bait—and products will sell, then thinking is too simple.
As already mentioned, hydraulic technology has a history of more than two hundred years, meaning others’ great-great-great-great-grandfathers had already begun R&D and had inheritance, while you, or your parents’ generation, just began learning. Being temporarily inferior to others is completely understandable. In this situation, reverse engineering and imitation as the first step in beginning R&D is completely acceptable, provided it doesn’t infringe intellectual property rights.
But one must clearly recognize that obtaining drawings through reverse engineering is only the beginning of R&D and should never be the end of R&D.
Because reverse engineering of component geometric dimensions is always conducted at normal temperature and pressure and cannot reflect the condition of components under pressure and non-normal temperature states. Moreover, reverse engineering at most measures a limited number of components; allowable deviations also cannot be measured.
Some units bought complete original drawings and process cards from Rexroth years ago. Forty years have passed, yet their products still haven’t reached the level of original products, which is proof.
A technical leader at Bosch Rexroth told me face to face: “Frankly speaking, much knowledge and skill for handling practical problems is not and cannot be expressed one by one in drawings. Rexroth’s product quality is guaranteed by the rich experience of dozens of technicians throughout the entire line from raw material inspection, processing, heat treatment, precision machining to assembly.”
Since even original drawings are not enough, those obtained through reverse engineering are even less adequate.
To truly make hydraulic valves that are influential, have markets, and thus have certain profits and sustainable development, there are many, many things to do.
In fact, if one lacks the ability to innovate, that’s okay. Researching existing products thoroughly, doing them well, continuously testing and improving can also occupy a place in the market.
Hydraulic technology has been in practical use for more than two hundred years. There are almost no hydraulic valves that haven’t been invented yet! But on the other hand, materials, processing techniques, fixtures, assembly processes, yield rates, sales channels, etc.—who can say they have reached optimum with no room for improvement?
China’s hydraulic valve production is mostly reverse engineering and imitation! If one understands principles, grasps essence, understands weaknesses, thinks of ways to overcome them, understands needs, one can improve according to needs. Improvement is also innovation!
Some Chinese enterprises manufacture hydraulic valve components as OEMs for domestic and foreign enterprises, with mature processes and high qualification rates. Now they plan to make hydraulic valves themselves. That’s fine! But one must clearly recognize: OEM qualification only means that the geometric dimensions of processed parts and heat treatment consistency have passed. This is the foundation for excellent hydraulic valve performance, but not all of hydraulic performance! When doing OEM work, customers buy your geometric dimensions; when making hydraulic valves yourself, your customers want to buy hydraulic performance!
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