The assignee ranking for this dataset is a long tail dominated by Chinese hydraulic-component manufacturers and equipment groups, alongside a university filer and several single-patent entrants. No assignee holds a commanding share of the 125 records tracked, and the strongest co-filing relationship — between a Japanese hydraulic-press specialist and a major steelmaker — spans just two shared filings. This is a fragmented field rather than one led by a small number of dominant portfolios.

Filings peaked at 16 in 2019, sat at 10 by the 2022 midpoint, and had fallen back to 2 in the latest partial year tracked. That trajectory looks like a plateau or mild decline rather than sustained growth, though the most recent one to two years are always undercounted because publication lags filing by roughly 18 months. Treat the very last data point as a floor, not a final answer.

China accounts for 110 of the 125 receiving-office filings in this dataset, far ahead of Japan, South Korea, the United States, the EPO and the United Kingdom, which together make up the remainder in single digits. This concentration reflects where hydraulic-component manufacturing and testing-equipment supply is centred for this specific claim scope. A search strategy limited to US or European filings alone would miss most of the documented activity.

US20240141931A1, filed by Zhejiang University, describes a constant-value method for detecting and evaluating internal leakage in a hydraulic cylinder. It works by measuring an accurate pressure drop across a hydraulic stroke and comparing that value against a defined standard parameter to judge whether the cylinder meets specification. It is a measurement-and-evaluation method claim rather than a hardware design claim, so it is most relevant to anyone building leak-detection logic around pressure-drop thresholds.

Inside this search scope, the dense claim territory is test-rig and pressure/leak-measurement instrumentation under G01M, which carries the largest share of records. Comparatively thinner areas include servo-valve leak-rate calibration, in-line dimensional inspection during cylinder assembly, and multi-axis actuator performance QC. These branches sit within the same IPC classes but show less filing density, making them worth checking closely before assuming the space is occupied.