In This paper experimemtal results concerning the delay time of cavitation in hydraulic fluids for stepwise reduction in parr from atmospheric pressure to a given pressure are presented. In the same way as in a previous paper, the fluid under study is enclosed in the annulus between two concentric cylinders, the inner one being rotating and the outer one at rest.
1) In case of a paraffin based oil, the delay time is experimentally obtained for speeds of the inner cylinder in between 100 and 1000 rpm, pressures P₁, between 140 and 700 mmHg, a fluid temperature θ of 40°C±1 deg and Reynolds mumbers Re determined by the width of the gap and the peripheral velocity of the inner cylinder between 72 and 718. As n is increased, and as P₁, decreases, the delay time shortens. The delay time calculated on the bans of the diffusion theory woes approximately with experimental result in the high speed range but not in the low speed range.
The particulate oontaminatiom level of the oil is 0.11 mg/ 100 ml of ARP 785. In this connection, a few experiments were performed on ailk, the contamination leavels of which were changed by adding AC test dust up to a level of 3.5 mg/100 ml. However, no puticular effect on the delay time was observed.
2) In addition to various petroleum based hydraulic fluids, water-glycol fluids, phosphate ester and tap water were also tested. The test were carried out with n= 400 rpm. P₁ from 140 to 450 mmHg, θ=40°C±1 deg and Re =220. For the tap water θ and Re were modified to 30° and 1.08 × 10⁴ reapectively.
The longest delay time for incipient cavitation was obtained for water-phycol fluids and the second longest was for tap water. Petroleum based hydrosdic fluids and the phosphate ester have almost same delay tines, which are slightly longer than that for the paraffim based oil.

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