There are highly reliable liquid cooling systems that use aerospace quality fitting and high-pressure hoses. These are too expensive for most users. These systems normally run at 20 psi, but they are designed to withstand 300 psi. The reason for this is water hammer, where if someone shuts off a valve or disconnects a shut off connector on a running system with a long piping run, the momentum of the coolant can turn into a pressure spike.
Negative pressure systems don’t create these kind of pressure spikes because the tubing used is very resilient and the coolant during startup has many bubbles in it. Also, the racks don’t use shut off connectors. The Chilldyne system lets air into the coolant system when it shuts down, so that when it restarts there are no worries about water hammer.