U.S. Navy Ship Salvage Manual Volume 6 - Oil Spill Response

S0300-A6-MAN-060with minimum inertia. A number of specially designed inlet heads are available, such as theadjustable weir skimmer shown in Figure 5-4.Figure 5-4. Self-Adjusting Skimmer/Inlet.Oil and water can be separated at the interface because of the differences in viscosity and specificgravity between oil and water. Oil floats on water because of its lower specific gravity. Becauseof the difference in viscosity between oil and water, there is a natural shear in a flowing mixtureof the two liquids. The more viscous oil can be induced to flow at a faster rate over or under a barrieror weir, placed at the oil-water interface by forces created by pump suction. The weir height isadjusted to allow only oil to flow over the weir and into the pump. The pump also transfers the oilfrom the weir into holding tanks or bladders.Suction devices are manufactured in a wide variety of sizes, from small portable units to largesystems incorporated into vessels. Modified or unmodified suction dredges can skim oil by holdingthe drag head at the water surface.Suction-weir-type skimmers are easily clogged by debris. Small units do not function well withhigh-viscosity and emulsified oils. Suction skimmers generally have a high recovery rate but lowrecovery efficiency because they do not discriminate well between oil and water.5-2.3 Induction Devices. Induction systems are usually built into vessels. The vessel moves intothe oil slick so that oil flows into an enclosed area where the effects of waves and current arereduced. Oil is separated at the interface or from the water surface with the following generaltypes of systems:5-6