They look like some kind of pressure control valve, the symbols at least look like a combination of a pressure relief and a pressure reducing valve. I'm not sure exactly what they are however. Hopefully that gives you a starting point for some research (or someone more knowledgeable comes along). Here's some links that you might find useful: How To Interpret Pressure Valves Pressure Relief and Regulating Valves
A pilot-operated to open check valve. Downstream pressure holds it closed. Upstream pressure opens it. The one on the left has a drain to tank. The one on the right has both a spring and dowstream pilot to close it.
No guessing here on the second symbol, it is what it is.
Note: that a Pilot operated valve Can use the process pressure from the #2 line, which may not be considered external. See the sun link for various examples.
First of all, questions like this can never be answered properly when the valves are cut out of context.
This is also a typical "student question" from someone trying to "learn" and a lot of answers are coming from people are "guessing" which of course creates a debate.
Any valve out of context can be analyzed differently because we all have different experiences. from symbol applications.
Another problem is that there is no exact 100% commonly used standard of symbol drawings and neither there is a 100% commonly used standard of interpreting and putting symbols into system context.
Neither one of these two valves can be considered "pilot operated" since there is no external pressure signal line involved in the symbols.
The valve to the left needs more "context" and the origin of the source. As drawn I have never seen it before. The valve to the right is as I interpret it drawn as a pressure relief valve. The control line from spring side to the B port is a drain function.
Pressure relief valves are NORMALLY CLOSED and drain to the tank.
Pressure reducing valves are NORMALLY OPEN and supply a downstream part of the system with lower and reduced pressure. As an example, the pilot lever control system in an excavator.
Hello
The symbol on the right is a two way valve. Normally open. Solenoid operated to Close the flow.
The other symbols do not look like they belong there, maybe a drafting error.
