1. Use Patent Databases: Utilize patent databases such as Google Patents or the United States Patent and Trademark Office (USPTO) database. These databases allow you to search for patents by keywords, inventors, assignees, patent numbers, and other criteria.

2. Search with Keywords: Enter relevant keywords such as “valve locking device,” “valve security,” “lockout device for valves,” or specific terms related to the type of valve or locking mechanism you're interested in.

3. Use Classification Codes: Look for the classification codes associated with valve locking devices. For example, the classification code “F16K” relates to valves; taps; cocks; actuating-floats; devices for venting or aerating. You can use these codes to refine your search.

4. Review Cited Patents: Examine the patents you've already found and review the patents they cite, as well as the patents that cite them. This can lead you to related patents.

5. Analyze Abstracts and Claims: Read the abstracts and claims of the patents you find to determine their relevance. The claims section is particularly important as it defines the scope of the patent's protection.

6. Consult a Patent Attorney: If you need assistance or a more targeted search, consider consulting with a patent attorney. They can help navigate the complexities of patent databases and legal jargon.

Remember, patent searching can be complex due to the technical language and legal nuances, so take your time to familiarize yourself with the process and the resources available.