delivered the opinion of the Court:

We agree with the tribunals below that the Williams’ structure is capable of ■ being operated with a liquid under high *589pressure; lienee every element of claim 3 is readable on the prior device.

Claim I calls for a cheek valve for each end of the vent pipe and a float for each valve, while Williams shows merely a float which also acts as a check valve. It is contended that the float of Williams will not prevent the hack flow of a liquid under pressure. This contention was not sustained in the Patent Office, where it was held properly, we think, that the float of Williams is capable, or may be made capable without the exercise of inventive skill, of withstanding such back pressure, and that the use by appellant of a check valve with a float therefor is but the substitution of one well-known equivalent for another.

It is next contended that the claim under consideration calls for a “four-way” valve, while the Williams’ patent specifies a “two-way” valve. Though these valves are called by different names, in structure they are substantially the same. The next difference alleged is that this claim demands that the supply and discharge pipes he unobstructed. In the Williams’ patent, floats are described situated within the cups at the ends of the supply and discharge pipes, which would probably, as claimed by appellant, bo forced against their seats by liquid under pressure, thus preventing the operation of the device. But the purpose of these floats is to prevent, hv means of locking devices with which they are connected, the turning of the handle carrying the valve in the supply and discharge pipes of the cups, until one of the cups is entirely empty and the other entirely Ml. It would ThquiTO hut the cxctcísc oí mese mechanical skill to remove these floats. The omission of this element, with a corresponding loss of function, does not amount to invention.

In regard to claims 5 and 6, we agree with the Board of Examiners in Chief, who said: “Claim 5 provides that the floats which close the vents shall he actuated by high pressiire only. Williams’ floats, so far as perceived, will he operated by either high or low pressure. Jt is not understood wherein there could he any invention in modifying these floats so that they could be operated only by high pressure., This claim, therefore, *590was also rightly rejected. Claim 6 involves merely'the considerations hereinabove discussed, and was also rightly rejected.”

Claims 7 and 8 provide that the floats shall be hemispherical and of large capacity. We are unable to discover invention in merely altering ’the size and shape of an element described in a patented device, where the difference in function is one already well known in the art.

The decision of the Commissioner of Patents is affirmed, and the clerk is directed to certify thesh proceedings as bjr law required. ' Affirmed.