Gauge Cock vs. Manifold

Sounds like a classic case of tomatoes verses tomotoes

Why not request drawings of both so you can make a better informed decision.

The gauge cock is simplest and cheapest. it allows the gauge to be removed without de-pressurising the process line. usually the cock is screwed into the line, the outlet of the cock is matched to the gauge and the gauge fitted directly. Problems: 1. Vibration in the piping will destroy the gauge eventually. 2. Installation is cheap, getting it to be visible can be difficult. 3. Pulsations in the fluid will destroy the gauge eventually. Solution: 1 and 2. take a line from a cock at the test point to where the gauge can be sensibly mounted. 3. go for the glycol filled option which dampens the needle movement. Manifold Mounting the Gauges. Here the lines are taken to a common manifold which has valves (cocks) built into it. Another line is then taken to the gauge panel where several gauges can be mounted, labelled and presented nicely. it is still a good idea to put a gauge at the take-off point in case of damage to the line to the manifold. Where gauges are to be mounted on vibrating pumps it is usually necessary to use a stiff line formed in two loops to the gauge, isolating the gauge from the vibration.

In this context, a "cock" is simply a single valve, whereas a manifold entails two or more valves. Terms vary according to local custom.

I think that historically the term "gauge cock" referred to each of the three test valves on the liquid column of a boiler. If the liquid is at the correct level, the upper valve willl emit (nearly) dry steam, the lower valve water, and the middle valve a bubbly mixture. This serves as a check on the automatic float switches. The best literary description of this is from Mark Twain's Tom Sawyer. Just before getting roped into fence painting, Tom's friend Ben comes down the street, pretending to be a steamboat....

A "cock" is a type of valve design. Distinct from ball valves, globe valves, butterfly valves, and knife gate valves, it features a conical plug with a hole drilled through it.

Common cocks are petcocks and seacocks. They are simply valves of a particular design.

The pressure gauges should be provided with these so that the gauge can be isolated and thus removed for replacement or repair.

The term "manifold" is the hydraulic equivalent of the the electrical term "bus."

I suspect that the term "manifold" is a special meaning applied by the supplier. You should ask him to explain.

Your designer was correct. Pressure gauges should be complete with isolating valves.

Follow the P&ID.

A gauge cock is nothing more than a shutoff valve used to isolate the gauge. A manifold is a device with one inlet port and two or more outlet ports. Each outlet port connects to other parts of the system by way of a valve to control flow through that part of the system. A gauge could be used on one of the manifold outlets. The designer is probably thinking about current needs. Your vendor is probably thinking of future expansion where a manifold would be needed. If this is the case, the manifold would use one port for the gauge and the remaining ports would have removable plugs in them.