The PL30 is a pressure limiter. It can be used to protect a sense line or low volume piece of equipment from overpressure.
The PL30 features a body with a 4000 psi rating, and an adjustable pressure limit up to 300 psi. Once the pressure limit is reached the PL30 closes to prevent over pressure. It reopens once the pressure goes back below the limit.
The PL30 is typically used to protect the sense line on a PC48 pressure pilot