Yes. As a first approximation we can use Bernoulli equation, which states that 0.5V^2+gz+p/rho [1] remains constant through a streamline. If we assume incompressible flow, no friction, perfect discharge, no altitude change etc., and that speed in the pressurized reservoir is null, we can obtain that p_reservoir = 0.5 V^2+p_ambient and thus V = sqrt(2(p_reservoir - p_ambient)) if I'm not mistaken.

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[1] Where V=velocity, g=gravity accel., z=height, p = pressure, rho=density