Reversing Polarity for Valves

Hi, I am building a manifold which houses 24 valves. Each valve 5V to actuate and latches and stays in this position until it is connected to 5V of reverse polarity. I have 12 digital outputs, and am currently using DPDT relays to switch polarity to the valves resulting in 24 relays - clearly not the most optimal solution. Is there a better way of doing this?

Thanks, John

You can substitute IC chip H-Bridges for the relays. An H-Bridge is after all just a DPDT switch. It would take two port pins per valve, unless you use an RC differentiator to create pulses off the port pin level change.