I require a 1/4" BSP female plastic solenoid valve.  It needs to be 12vDC, and to have minimal exposed metal (preferably none as the marine environment will kill it quickly).Globe Valves  The challenging part is it must be NORMALLY OPEN.  It must also be cheap (<8USD - purchasing 200 PA).

Using the ASME system in this regard is A LOT simpler in that one can simply state - Class 150# as per ASME B16.5 Table 2..... etc. when specifying a valve. Proof of compliance with this is then up to the manufacturer. Also ensuring that you are specifying something that meets both the pressure and temperature conditions you require is then taken care of.

Most of the components that I am specifying fall into Class 0 of the PED with a limited number falling into Class ISafety valves . In other words they only require sound engineering practice in terms of their design - with those in Class I not requiring a CE marking as far as I understand.

So if I understand you correctly what you are saying is:
Ensuring p/T compliance using the EN 'method' would then require specification of a nominal rating of PN16 (for example) and going out, finding products that comply with this spec.Plug Valves Then requesting p/T curves for the product/s and ensuring that the product meets the worst case scenario (WCS) for p/T that you are trying to cater for.Reducing Valves Alternatively you could state what your WCS is then go out on enquiry with that p/T information - which means that you may end up getting a valve with a nominal pressure rating of PN40 in order to meet the pressure requirements at elevated temperature.
Either method requires the PN rating to be updated on the datasheet based on the limitations of the final chosen product - unless you get it right first time; with the first requiring considerably more work in terms of picking the final chosen product.

Now - before I look like one of the guys on these forums trying to get a quick and easy solution - I am not trying to get out of doing the work by any means - my basic problem is trying to figure out the industry standard way of specifying the pressure rating of valves to EN specifications so that I can ensure I get the same thing every time with minimal trawling through the limitless number of valves available out there.

A technical warning:  a pity you have to be careful about your full application here, but salt water, salt sprey and air in combination handeled directly by a solenoid valve is an unfortunate combination.Balance Valves Even if innards are fully protected and sealed, salt crust can form and damage your operation.

I would advice you to have a look into miniature diaphragm valves in all plastics (does exist-check the sites above) air operated over air solenoid valves, and protected by checkvalves to avoid seawater coming in the wrong way

This will probably be m more troublefree and have a longer maintenance free lifetime, but the combination will burst your small bag of money.....

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