Hydraulic Valve Production Testing

Types

1. Testing of raw materials and purchased parts.
2. Testing of parts and components during production (mainly processing dimensions, shape and position errors).
3. Testing of assembled hydraulic valves (conducted before entering finished product warehouse, commonly called “factory inspection”).

Factory inspection is the various inspections before product delivery, including assembly and appearance inspection, performance inspection, with the core being performance inspection completed through factory testing.

It must be recognized that: factory inspection is “inspective” in nature, can only detect defective products and reduce the probability of non-conforming products flowing out, but cannot guarantee that inspected products have no defects (no inspection can 100% screen out problems in all aspects).

Purpose of Factory Testing

1. Setting: Set pressure for relief valves and pressure reducing valves, flow for flow control valves, etc. according to customer requirements.
2. Detect important performance: Verify compliance with factory standards. Factory inspection workload is large; if the manufacturing process is stable, partial items can be sampled according to industry standard recommendations (see Section 7 of this section: Acceptable Quality Limit).
3. Flushing: Utilize testing opportunity to flush internal flow passages (contamination may still remain after assembly), seal and package after testing to reduce contaminant entrainment. Cleanliness is crucial for hydraulic valves, therefore even if some performance items are sampled, 100% “oil passage” (oil flushing) should still be conducted.

Factory Testing Items

JB recommends functional items for factory testing; manufacturers need to determine specific items based on production process, product importance, etc.

Some JB standards require sampling inspection of pressure resistance testing for factory testing, but equipment and energy consumption costs are high. If type testing has already conducted pressure resistance testing and raw material quality and manufacturing process are stable, factory testing can be exempted from pressure resistance testing (world-class companies also often do not conduct it).

Test Bench Design

When designing factory testing circuits and test benches, production program must first be clarified, testing time estimated (including clamping and disassembly), with key focus on “high efficiency, low cost”, for example:

1. Convenient clamping.
2. Comprehensive design of test circuits, completing all tests in one clamping as much as possible.
3. Equipped with sufficient safety protection measures.
4. Emphasize oil contamination control: test bench equipped with multiple large capacity dirt-holding filters, regularly inspect and record oil contamination status according to GB/T 14039.
5. Accuracy of measuring instruments can be appropriately reduced compared to R&D testing.

Test Task Sheet

Factory test task (plan) sheet should include at least:

1. Product to be tested, code.
2. Test items.
3. Test circuit.
4. Test method.
5. Qualification criteria.

Test Report

Due to large product volume, only important, high-performance components (such as servo valves, safety valves inspected by specialized institutions) need separate test reports.

The key is to promptly analyze test conditions, compile statistics on non-conforming product deviation classifications, to provide basis for identifying defect causes, improving production management, and reducing defect rate —— reducing defect rate means reducing costs and increasing profits; only by reducing factory inspection defect rate can delivery defect rate and early usage defect rate be reduced.

Sampling Inspection

Because factory inspection involves large numbers of workpieces, qualified products constitute the majority but it is impossible to have absolutely no defects, hydraulic valve JB recommends sampling according to GB/T 2828.1 “Sampling Procedures for Inspection by Attributes – Part 1: Sampling Schemes Indexed by Acceptance Quality Limit (AQL) for Lot-by-Lot Inspection” (ISO 2859-1), with the general process being:

1. Determine sample size code letter according to lot size and general inspection level.
2. Determine the number of randomly selected samples based on sample size code letter.
3. Conduct inspection.
4. Based on inspection results and referring to standards, decide whether to accept the entire lot.
5. Adjust inspection status according to actual situation: Normal inspection N, Tightened inspection T, Reduced inspection R, Discontinuation of inspection D.