Where is a union generally installed in a piping system?

In a piping system, a union is generally installed downstream of a valve. This placement allows for convenient disconnection and maintenance of the piping system without having to remove the entire valve. When a valve is shut off, having the union downstream enables the technician to access the pipe section more easily by unscrewing the union, thereby ensuring that the system can be serviced without disrupting the flow or the integrity of the upstream connections.

Placing a union upstream of a valve can complicate disassembly for maintenance since it might involve dealing with any residual pressure within the valve itself. Installing a union in the middle of a pipe run or at the beginning of a pipeline would not provide the same level of flexibility for servicing the system, as these locations are not ideal for isolating sections of pipe effectively. Hence, the most practical and effective placement for accessibility and safety in routine maintenance is downstream of the valve.