Abstract: The present invention relates to a delivery tube array which is used to connect a patient to a patient ventilator. A problem arising in such use of patient ventilators is that exhaled air cannot be exhausted directly to the atmosphere since a normal outlet valve would also serve to exhaust air delivered on the compression stroke of the ventilator. The invention overcomes this problem by the introduction into a delivery tube array of a relief valve, a non-return valve 12 and a bleed-pipe which connects the relief valve to a point up-stream of the non-return valve. Such an arrangement ensures that the relief valve opens only when the pressure within the patient's lungs is greater than the pressure upstream of the non-return valve.