An illustrative modular manifold system includes, among other things, two or more modular pump manifolds, a low-pressure header, and a main high-pressure manifold. Modular pump manifolds may include a low-pressure manifold for supplying fracturing fluid or water to pumps, a high-pressure manifold for supplying fracturing fluid or water to one or more wells and a bleed-off/prime-up manifold. Each modular pump manifold of the modular manifold system is configured to be fluidly isolatable from the other modular pump manifolds. Each isolated modular pump manifold is configured to be flushed with water, bled off and primed up independently of the other modular pump manifolds. After the bleed off, maintenance procedures may be performed on pumps associated with the isolated modular pump manifold. The modular pump manifolds that are not isolated may continue in active fracing stage operations while a modular pump manifold is isolated.