Depends on the manufacturer's standards.vng21092 wrote:How safe is this?
You might eventually screw up the seals and cause leaks but it's unlikely to explode. The brass valves from Harbor freight are rated for 600 but can fail around 1000psi (personal experience).
You can probably find a more suitable valve on ebay for under $20, look for a 1/4" stainless or hydraulic equivalent.