std::equal_range Behaviour

Thanks in advance;

What I'm trying to do is find all the elements in the map that have a
certain value. The question I have is can you do this when the value
you are trying to find is not in the key of the map? The code seems to
work except that when I iterate through the result I end up getting
values that don't match the criteria.

Is there another algorithm that I should use instead? For instance,
can I use find_if in a while loop or something like that?

Here is a snippet of the code:

class ChannelFields
{
public:
    long lngPortId;
}

class CompChannelPortId
{
public:
    CompChannelPortId() {}
    bool operator() ( const std::pair<long, ChannelFields>& lhs, const
std::pair<long, ChannelFields>& rhs ) const
    {
        return( lhs.second.lngPortId < rhs.second.lngPortId )
    }
};

class ChannelDbMap : std::map<long, ChannelFields>
{
public:
    void
    refreshMap( long id )
    {
        std::pair<long, ChannelFields> compChannel;
        compChannel.second.lngPortId = id;
        std::pair<iterator, iterator> range
                = std::equal_range( begin(), end(), compChannel,
CompChannelPortId() );
    }
}