Steam blowing sacrificial valve

I'm working on steam blowing of co generation plant. I have observed three different location of sacrificial valve in various past project design.

1. To locate the sacrificial valve at the upstream side of the target plate.

2. To locate the sacrificial valve at the downstream side of the target plate.

3. To locate the sacrificial valve near to heat source.

What criteria decides location of the sacrificial valve?

Thanks

I've work an afew co-gen plants before and NEVER have I encountered the term "sacrificial valve"! Could you please elaborate as to the function of this valve?

Dear 11echo,

I am sorry for my wrong terminology. I am taking about the valve which controls(start/stop) steam flow for blowing.