How to Volume Render Data in Custom Application Without Widgets?

Hello experts,
I am writing a custom application to load in .pvd data and then volume render it. I am able to load in the data, and display at as representation types Surface, Points, Outline etc. But when I set it to Volume, nothing is rendered on the screen although the data is loaded.

This is how I load the data:

QStringList files;
files << /path/to/data/;
pqPipelineSource* pipelineSource = pqLoadDataReaction::loadData(files, "sources", "PVDReader");

This is how I create the representation and render it:

pqObjectBuilder *builder = pqApplicationCore::instance()->getObjectBuilder();
pqDataRepresentation *drep = builder->createDataRepresentation(pipelineSource->getOutputPort(0), view);
auto dProxy = drep->getProxy();
vtkSMPropertyHelper(dProxy, "Representation").Set("Surface");

Am I missing something?
Thank You