pump.io port in URL

I just installed pump.io on my server (CentOS 6.5, x64), and I also have a Ghost blog (blog.mydomain.example) hosted on my server, which is behind Apache. The home page of my site is a static html page.

Now the problem is: when I visit social.mydomain.example, I'll be redirected to my blog (the URL is still social.mydomain.example). I can only visit pump.io by entering social.mydomain.example:31337 and the user link would be something like social.mydomain.example:31337/test. How can I make the port number disappear in the URL and visit pump.io via social.mydomain.example? Thanks!

Here are some configurations on my server:

Apache host settings:

<VirtualHost *:80>
    ServerName blog.mydomain.example
    ProxyPreserveHost on
    ProxyPass / http://127.0.0.1:2368/
</VirtualHost>

<VirtualHost *:80>
    ServerName  mydomain.example    
    ServerAlias www.mydomain.example 
    ProxyRequests off
    DocumentRoot /var/www/html
</VirtualHost>

How I installed pump.io

cd /usr/bin/nodejs/
git clone https://github.com/e14n/pump.io.git
cd pump.io
npm install

cd pump.io/node_modules/databank
npm install databank-mongodb

cd /usr/bin/nodejs/pump.io/bin
forever start pump

My pump.io configuration

cat /etc/pump.io.json

{
    "driver":  "mongodb",
    "params":  {"host": "localhost"},
    "secret":  "pumpiol",
    "noweb":  false,
    "port": 31337,
    "site":  "social.mydomain.example",
    "owner":  "NetAdmin",
    "ownerURL":  "http://mydomain.example",
    "hostname":  "social.mydomain.example",
    "nologger":  false,
    "serverUser":  "pumpio",
    "uploaddir": "/var/local/pump.io/uploads",
    "debugClient": false,
    "firehose": "ofirehose.example"
}

My iptables configuration

-A INPUT -m state --state NEW -m tcp -p tcp --dport 31337 -j ACCEPT

My DNS zone file:

A (Host)
Host    Points To   
@   M.Y.I.P
CName (Alias)
Host    Points To
blog    @   
social  @   
www @