google map marker image sprite - google-maps-api-3

Question

This is my first post here, hope someone can help.
I am building a mapping website using google maps.
The map shows upto 14 different icons based on a type category
I understand the theory of sprite images and the reduction in server calls these have so I have one image conating all the markers.
Question:
How do I set the position of the sprite, but only call the image once?
I have seen this post
Google map marker sprite image position
but that only shows changing the image for one marker
This is the code
//set the image once
var img = {
url:'images/site/type_sprite.png',
size: new google.maps.Size(32,32),
origin: new google.maps.Point(0,0)
};
idx = 0;
for (var i = 0; i < l; i++) {
lat = parseFloat(markers[i].getAttribute("lt"));
lng = parseFloat(markers[i].getAttribute("ln"));
var type = markers[i].getAttribute("typ");
if ((lat < latUpper && lat > latLower) && (lng < lngUpper && lng > lngLower) && (jQuery.inArray(type,filter_arr)>=0)) {
//change the position of the icon sprite depending on type
switch(type) {
case 'AA':
img(origin, new google.maps.Point(0,0));
break;
case 'AC':
img(origin = new google.maps.Point(0, 42));
break;
case 'ACF':
img(origin= new google.maps.Point(0,84));
break;
default:
img(origin= new google.maps.Point(0,0));
}
var id = markers[i].getAttribute("id");
var name = markers[i].getAttribute("nme");
//var icon = 'images/pins/' + type + '.png';
var point = new google.maps.LatLng(lat, lng);
var marker = new google.maps.Marker({
map: map,
position: point,
title: name,
icon: img
});
//add to valid array
markersArray.push(marker);
//build infowindow string
str = '<div class="iw_h">' + id + ' ' + name + '</div>';
bindInfoWindow(marker, map, infoWindow, str);
bounds.extend(point);
map.fitBounds(bounds);
idx++;
}
} //end of loop
}
If I put the code
var img = {
url:'images/site/type_sprite.png',
size: new google.maps.Size(32,32),
origin: new google.maps.Point(0,0)
};
inside the loop, doesn't that mean the image is repeatedly downloaded (and it will be a bigger image than an individual icon) thus defeating the object of using a sprite?
This is the site btw
http://www.searchforsites.co.uk/full_screen.php